Add support for tagless streams?

[brian-arnold]

After preparing a dataframe called 'df', the following doesn't work:

pipeline_in = op.DataFrameSource(df) # this fails when running pipeline_in to view contents
pipeline_in

With an error message that doesn't explicitly/directly refer to the fact that there are no tags:

---------------------------------------------------------------------------
ArrowInvalid                              Traceback (most recent call last)
File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/IPython/core/formatters.py:406, in BaseFormatter.__call__(self, obj)
    404     method = get_real_method(obj, self.print_method)
    405     if method is not None:
--> [406](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/IPython/core/formatters.py:406)         return method()
    407     return None
    408 else:

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/base.py:477, in StatefulStreamBase._repr_html_(self)
    476 def _repr_html_(self) -> str:
--> [477](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/base.py:477)     df = self.as_polars_df()
    478     tag_map = {t: f"*{t}" for t in self.tag_keys()}
    479     # TODO: construct repr html better

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/base.py:375, in StatefulStreamBase.as_polars_df(self, include_data_context, include_source, include_system_tags, include_content_hash, sort_by_tags, execution_engine, execution_engine_opts)
    361 def as_polars_df(
    362     self,
    363     include_data_context: bool = False,
   (...)    369     execution_engine_opts: dict[str, Any] | None = None,
    370 ) -> "pl.DataFrame":
    371     """
    372     Convert the entire stream to a Polars DataFrame.
    373     """
    374     return pl.DataFrame(
--> [375](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/base.py:375)         self.as_table(
    376             include_data_context=include_data_context,
    377             include_source=include_source,
    378             include_system_tags=include_system_tags,
    379             include_content_hash=include_content_hash,
    380             sort_by_tags=sort_by_tags,
    381             execution_engine=execution_engine,
    382             execution_engine_opts=execution_engine_opts,
    383         )
    384     )

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/sources/base.py:384, in SourceBase.as_table(self, include_data_context, include_source, include_system_tags, include_content_hash, sort_by_tags, execution_engine, execution_engine_opts)
    373 def as_table(
    374     self,
    375     include_data_context: bool = False,
   (...)    381     execution_engine_opts: dict[str, Any] | None = None,
    382 ) -> "pa.Table":
    383     """Delegate to the cached KernelStream."""
--> [384](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/sources/base.py:384)     return self().as_table(
    385         include_data_context=include_data_context,
    386         include_source=include_source,
    387         include_system_tags=include_system_tags,
    388         include_content_hash=include_content_hash,
    389         sort_by_tags=sort_by_tags,
    390         execution_engine=execution_engine,
    391         execution_engine_opts=execution_engine_opts,
    392     )

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/kernel_stream.py:190, in KernelStream.as_table(self, include_data_context, include_source, include_system_tags, include_content_hash, sort_by_tags, execution_engine, execution_engine_opts)
    186 self.refresh()
    187 assert self._cached_stream is not None, (
    188     "Stream has not been updated or is empty."
    189 )
--> [190](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/kernel_stream.py:190) return self._cached_stream.as_table(
    191     include_data_context=include_data_context,
    192     include_source=include_source,
    193     include_system_tags=include_system_tags,
    194     include_content_hash=include_content_hash,
    195     sort_by_tags=sort_by_tags,
    196     execution_engine=execution_engine,
    197     execution_engine_opts=execution_engine_opts,
    198 )

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/table_stream.py:239, in TableStream.as_table(self, include_data_context, include_source, include_system_tags, include_content_hash, sort_by_tags, execution_engine, execution_engine_opts)
    235 try:
    236     target_tags = (
    237         self._all_tag_columns if include_system_tags else self._tag_columns
    238     )
--> [239](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/orcapod/core/streams/table_stream.py:239)     return table.sort_by([(column, "ascending") for column in target_tags])
    240 except pa.ArrowTypeError:
    241     # If sorting fails, fall back to unsorted table
    242     return table

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/pyarrow/table.pxi:2157, in pyarrow.lib._Tabular.sort_by()

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/pyarrow/compute.py:269, in _make_generic_wrapper.<locals>.wrapper(memory_pool, options, *args, **kwargs)
    267 if args and isinstance(args[0], Expression):
    268     return Expression._call(func_name, list(args), options)
--> [269](https://vscode-remote+ssh-002dremote-002bdevenv.vscode-resource.vscode-cdn.net/home/barnold/enigma_repos/orcapod_pipeline/notebooks/~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/pyarrow/compute.py:269) return func.call(args, options, memory_pool)

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/pyarrow/_compute.pyx:399, in pyarrow._compute.Function.call()

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/pyarrow/error.pxi:155, in pyarrow.lib.pyarrow_internal_check_status()

File ~/enigma_repos/orcapod_pipeline/.venv/lib/python3.12/site-packages/pyarrow/error.pxi:92, in pyarrow.lib.check_status()

ArrowInvalid: Must specify one or more sort keys