fix(test): specify encoding=utf-8 reading BaseRobot.py/pyproject.toml

[petercorke]

Summary

• main itself is currently failing CI on every Windows job (confirmed via gh run list --branch main — latest run's conclusion is failure), which was also failing identically on every one of fix(mobile): guard VehicleDriverBase against workspace=None #541-fix(models): make KinovaGen3 load via robot_descriptions, add XACRO_ARGS support #546 since they all inherit from main.
• Root cause: tests/test_backend_capabilities.py opens BaseRobot.py (twice) and pyproject.toml with plain open(path) — no encoding specified. Windows defaults to the locale codepage (cp1252) rather than UTF-8. BaseRobot.py's docstrings contain a stylized Unicode math italic "𝜋" (U+1D70B), which cp1252 can't decode → UnicodeDecodeError on every Windows job, every PR.
• Fix: add encoding="utf-8" to all three open() calls. Confirmed these were the only unencoded open() calls in tests/.
• Note: macOS jobs on some of these PRs also show failures, but that's the already-documented, unrelated test_IK_GN3 numerical flakiness (tech-debt.md) — not touched by this PR.

Test plan

• pytest tests/test_backend_capabilities.py — 21 passed, 4 skipped
• Full suite: 652 passed, 13 skipped, no regressions
• Can't reproduce the Windows-specific default-codepage behavior on macOS directly, but the fix (explicit encoding="utf-8") is correct on every platform regardless — it's the only way to guarantee the file (an actual UTF-8 source file) decodes correctly no matter the OS locale.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (a9ed8d4) to head (6d064ed).
⚠️ Report is 42 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff           @@
##            main    #548    +/-   ##
======================================
  Coverage   0.00%   0.00%            
======================================
  Files        137     137            
  Lines      13690   13434   -256     
======================================
+ Misses     13690   13434   -256     

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