Improve testing of phlex Python annotations

[greenc-FNAL]

This PR improves the testing of plugins/python/python/phlex/__init__.py by adding unit tests for the MissingAnnotation exception. It covers the case where a required argument is missing from the annotations and verifies that optional arguments with default values do not trigger the exception. These changes bring the coverage of phlex/__init__.py to 100%.

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PR created automatically by Jules for task 8666460460076968556 started by @greenc-FNAL

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[Copilot]

Pull request overview

Adds unit test coverage for phlex.MissingAnnotation behavior as exercised through phlex.Variant, ensuring required-but-unannotated parameters raise and optional parameters with defaults do not.

Changes:

• Import MissingAnnotation into the Variant unit test module.
• Add tests verifying Variant(...) raises MissingAnnotation when a required parameter annotation is missing.
• Add tests verifying missing annotations for defaulted (optional) parameters do not raise.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #328      +/-   ##
==========================================
+ Coverage   80.20%   80.39%   +0.19%     
==========================================
  Files         127      127              
  Lines        3102     3102              
  Branches      547      547              
==========================================
+ Hits         2488     2494       +6     
+ Misses        386      381       -5     
+ Partials      228      227       -1     

Flag	Coverage Δ
unittests	80.39% <ø> (+0.19%)	⬆️

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see 2 files with indirect coverage changes

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