feat(sound): integrates sound tests and fixes Web Audio errors

[julianharty]

Integrates and refactors sound tests from https://github.com/commercetest/babylonjs-sound-testing repo which were created as for this purpose.

Adds comprehensive test coverage (59 tests) with audio utilities, integration tests, verification tests, and diagnostics. Note: there are still more tests available in the babylonjs-sound-testing repo that may be relevant. This commit is already large so I'd prefer to consider them once this work has been reviewed and merged.

Details:
Test Suite Changes:

• Add audio test utilities (FFT, RMS, tone generation, clipping detection)
• Add sound-integration.test.js (15 tests: lifecycle, async workflows, edge cases)
• Add sound-verification.test.js (24 tests: audio output, MIDI, instruments)
• Add sound-api-investigation.test.js (2 tests: API exploration)
• Add sound-replacement-diagnostic.test.js (3 tests: timing diagnostics)
• Update test infrastructure (tests.html, run-api-tests.mjs)

Bug Fixes:

• Fix NaN error in playNotes() when durations array shorter than notes
  • Add default duration (0.5 beats) for missing values
  • Add parameter validation in playMidiNote() to prevent non-finite values
  • Prevents "linearRampToValueAtTime non-finite value" Web Audio API errors
• Fix sound replacement tests to account for loop parameter behavior
  • Promise resolution timing differs: loop=true (immediate) vs loop=false (on end)

Test Organization:

• Integration tests: workflows, replacement, cleanup, spatial/non-spatial
• Verification tests: deep API validation, audio output, FFT analysis
• Investigation tests: document actual BabylonJS Sound API methods
• Diagnostic tests: sound replacement timing and promise behavior

Results: 59/59 tests passing, no Web Audio errors

Related to issue #264
documenting playSound() promise behavior and playNotes() array handling.