build: apply instrumented test dependencies conditionally

[jamesarich]

Check for the existence of src/androidTest before adding test-related dependencies in convention plugins. This prevents unnecessary dependency resolution for modules without instrumented tests. Additionally, removed unused test dependencies from the firmware feature module.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 7.94%. Comparing base (c234ace) to head (d91315f).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #4698      +/-   ##
========================================
- Coverage   8.12%   7.94%   -0.19%     
========================================
  Files         64      64              
  Lines       2499    2657     +158     
  Branches     289     309      +20     
========================================
+ Hits         203     211       +8     
- Misses      2264    2414     +150     
  Partials      32      32              

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