Add coverage tests for data coercion helpers

[Copilot]

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Adds focused test coverage for compas.data.coercion, one of the uncovered areas from the coverage report. The new tests verify normal tuple/list coercion, confirm the well-known string-as-iterable behavior, cover empty-sequence boundary cases, and assert the expected TypeError for non-iterable top-level inputs.

Checklist

• I added a line to the CHANGELOG.md file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke lint).
• I added new functions/classes and made them available on a second-level import, e.g. compas.datastructures.Mesh.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.46%. Comparing base (277cbba) to head (291637b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1518      +/-   ##
==========================================
+ Coverage   62.38%   62.46%   +0.08%     
==========================================
  Files         208      208              
  Lines       22486    22486              
==========================================
+ Hits        14027    14046      +19     
+ Misses       8459     8440      -19     

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