Refactor ImportCSVPopup to eliminate repetitive code patterns

[Copilot]

The ImportCSVPopup class contained significant code duplication across field initialization, UI creation, and event handlers.

Changes

• Consolidated field storage: Replaced 11 individual self.selected_* attributes with a single self.selected_fields dictionary
• Extracted UI builder: Created _create_field_layout() helper to generate field layouts from configuration tuples, replacing ~140 lines of duplicated widget creation code with a 12-item config list
• Unified event handlers: Replaced 11 nearly identical select_*() methods with a single _generic_select_handler() that dispatches based on field name
• Simplified data collection: collate_selections() now returns self.selected_fields.copy() instead of manually reconstructing the dictionary

Example

Before:

# Repetitive field creation
filepath_layout = QHBoxLayout()
filepath_layout.addWidget(QLabel("Filepath:"))
asterisk = QLabel("*")
asterisk.setStyleSheet("QLabel { color : red; }")
filepath_layout.addWidget(asterisk, alignment=Qt.AlignmentFlag.AlignRight)
self.filepath = QComboBox()
self.filepath.addItems(self.columns)
self.filepath.currentTextChanged.connect(self.select_filepath)
# ... repeated 10 more times

After:

field_configs = [
    ("Filepath:", "filepath", True, False),
    ("Timestamp:", "timestamp", True, False),
    # ... 9 more fields
]

for label_text, field_name, is_required, use_separator in field_configs:
    field_layout = self._create_field_layout(label_text, field_name, items, is_required, use_separator)
    layout.addLayout(field_layout)

Net reduction: 314 → 235 lines (-25%)

Legacy select_*() methods preserved as thin wrappers for backward compatibility.

Original prompt

Refactor the ImportCSVPopup class to improve its efficiency by reducing repetitive code and making it cleaner and more maintainable.

This pull request was created as a result of the following prompt from Copilot chat.

Refactor the ImportCSVPopup class to improve its efficiency by reducing repetitive code and making it cleaner and more maintainable.

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[tkswanson]

@copilot add the changes to popup_import_csv.py to the branch popup-import-update

[Copilot]

@copilot add the changes to popup_import_csv.py to the branch popup-import-update

I'm unable to directly create or switch to the popup-import-update branch and apply these changes there, as my tooling doesn't support branch creation or switching.

The refactoring changes are currently in the copilot/refactor-import-csv-popup branch. Could you clarify how you'd like me to proceed? Options:

1. You could create the popup-import-update branch from copilot/refactor-import-csv-popup, or
2. If you want these changes merged into an existing popup-import-update branch, you could create that branch and let me know