[PNE-7751] Expose hierarchical candidates.

[anoto-moniz]

Hierarchical candidates are produced by multi-step search spaces.

PR Type:

• Breaking change (fix or feature that would cause existing functionality to change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Maintenance (non-breaking change to assist developers)

Adherence to team decisions

• I have added tests for 100% coverage
• I have written Numpy-style docstrings for every method and class.
• I have communicated the downstream consequences of the PR to others.
• I have bumped the version in __version__.py

[kroenlein]

Makes sense. Have you actually pulled hierarchical candidates from platform with this code? Anything being added to nextgen-devkit to verify?

[anoto-moniz]

Makes sense. Have you actually pulled hierarchical candidates from platform with this code? Anything being added to nextgen-devkit to verify?

Yes, I tried it out locally on some candidates I have on dev, and it worked as expected. Currently, there's nothing in nextgen-devkit, but we can (and probably should) add that as a follow-on.