Use single attribute for location when making tracks layer

[cmalinmayor]

Proposed Change

Tracks layer construction now expects a single attribute containing the position on each node. This mirrors the new standard for candidate graphs created with motile_toolbox.

Checklist

Go through these things before merge. Actions should run automatically to test them, but for information on how to run locally, see CONTRIBUTING.md.

• I have added tests that prove that my feature works in various situations or tests the bugfix (if applicable).
• I have checked that the tests pass and I maintained or improved test coverage (if applicable).
• I have written docstrings and checked that they render correctly in the documentation build.
• I have checked that mypy type checking passes.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 83.90%. Comparing base (be7b3e9) to head (304792a).

Files	Patch %	Lines
src/motile_toolbox/visualization/napari_utils.py	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
- Coverage   85.06%   83.90%   -1.17%     
==========================================
  Files          12       12              
  Lines         288      292       +4     
==========================================
  Hits          245      245              
- Misses         43       47       +4     

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