Enhance Kokoro TTS Plugin with Comprehensive Features and Error Handling

[doroteaMonaco]

• Updated documentation in tts.rs and kokoro_wrapper.rs for clarity on audio chunk types and synthesis methods.
• Added detailed error handling tests in kokoro_error_handling_tests.rs to ensure robustness against various failure scenarios.
• Implemented comprehensive tests in kokoro_tts_tests.rs to validate synthesis, streaming, voice selection, and concurrent processing.
• Created a demo application in kokoro_tts_demo showcasing basic synthesis, streaming, voice enumeration, and error handling.
• Introduced mock implementations for testing without requiring actual model files, facilitating easier development and testing.

📋 Summary

• Updated documentation in tts.rs and kokoro_wrapper.rs for clarity on audio chunk types and synthesis methods.
• Added detailed error handling tests in kokoro_error_handling_tests.rs to ensure robustness against various failure scenarios.
• Implemented comprehensive tests in kokoro_tts_tests.rs to validate synthesis, streaming, voice selection, and concurrent processing.
• Created a demo application in kokoro_tts_demo showcasing basic synthesis, streaming, voice enumeration, and error handling.
• Introduced mock implementations for testing without requiring actual model files, facilitating easier development and testing.

🔗 Related Issues

Closes #

Related to #156

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🧠 Context

The Kokoro TTS implementation was complete but lacked:

1. Clear Documentation: Audio format specifications, supported voices, error handling patterns
2. Comprehensive Tests: No validation of synthesis correctness, streaming behavior, error cases
3. Usage Examples: No demo showing how to use the API effectively
4. Type Information: Unclear what audio formats are returned and how to process them

This PR provides production-ready documentation and test coverage to ensure reliability and ease of use.

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🛠️ Changes

Documentation Enhancements

• crates/mofa-plugins/src/tts/kokoro_wrapper.rs (+170 lines):
  • Module-level documentation with audio format specifications (PCM WAV, 16-bit, 24kHz, mono)
  • Supported voices documentation for v1.0 and v1.1 models
  • Voice name variants and fallback behavior
  • Error handling patterns and recovery strategies
  • Complete usage examples with code snippets
  • Thread safety and concurrency guarantees
  • Detailed method documentation for synthesize() and synthesize_stream()

Comprehensive Test Coverage

• crates/mofa-plugins/tests/kokoro_tts_tests.rs (330 lines, 13 tests):

  • WAV format header validation
  • Audio format verification (24000 Hz sample rate, 16-bit PCM depth)
  • Synthesis with varying text lengths
  • Empty text error handling
  • Multiple synthesis call tracking
  • Streaming callback invocation verification
  • Non-empty chunk delivery validation
  • Voice selection and fallback behavior
  • Concurrent synthesis (5 parallel tasks)
  • Audio format correctness checks

• crates/mofa-plugins/tests/kokoro_error_handling_tests.rs (369 lines, 17 tests):

  • Empty text rejection
  • Invalid UTF-8 detection
  • Network error handling
  • Text submission failure scenarios
  • Streaming error conditions
  • Unknown voice graceful fallback
  • Error message clarity validation
  • Error state isolation
  • Recovery from transient errors
  • Concurrent mixed success/error scenarios

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🧪 How you Tested

cargo clippy --workspace --all-features -- -D errors
cargo test --workspace --all-features
cargo build --examples
cargo doc --workspace --no-deps --all-features
cargo doc --workspace --no-deps --all-features --document-private-items

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📸 Screenshots / Logs (if applicable)

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⚠️ Breaking Changes

• [X ] No breaking changes
• Breaking change (describe below)

If breaking:

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🧹 Checklist

Code Quality

• [X ] Code follows Rust idioms and project conventions
• [ X] cargo fmt run
• [X ] cargo clippy passes without warnings

Testing

• [X ] Tests added/updated
• [X ] cargo test passes locally without any error

Documentation

• [ X] Public APIs documented
• [X ] README / docs updated (if needed)

PR Hygiene

• [X ] PR is small and focused (one logical change)
• [X ] Branch is up to date with main
• [X ] No unrelated commits
• X[ ] Commit messages explain why, not only what

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🚀 Deployment Notes (if applicable)

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🧩 Additional Notes for Reviewers

[lijingrs]

test error_handling_tests::test_error_is_descriptive_not_generic ... FAILED Test failed. Please make sure your code is up to date. Thanks.

[doroteaMonaco]

Sorry, thanks for the review! I pushed a fix for the failing test