feature: Additional unit tests for simplified TFE conversion API (pt. 2)

[ShrimpCryptid]

Continues work towards #44, reduce data script complexity. This change adds additional unit tests for the conversion API and a few minor fixes.

Estimated review size: medium, 20 minutes

Changes

• Fixes bugs and adds related unit tests.
• Adds error messages for invalid data (missing rows, missing features, only outliers, etc.)
• Adds new unit tests for frame generation validation and input handling:
  • [x] Frame generation
  • [x] Keeps bounds data during frame regeneration
  • [x] skips frame generation when frames already exist
  • [x] override switch works
  • [x] regenerates frames if number of objects has changed
  • [x] regenerates frames if one or more frames is missing
  • [x] regenerates frames if times data is missing or corrupted
  • [x] Parses aliasing for data column names
  • [x] Does not crash when missing optional centroid or outliers data
  • [x] Throws exception if no features exist
  • [x] Throws exception if no objects exist
  • [x] Uses object ID if track is not provided
• Changes ColorizerDatasetWriter to store output directories as pathlib.Path.