Fix plugin idempotency issue with React re-renders

[katspaugh]

Problem

Fixes katspaugh/wavesurfer.js#3731

The plugin instances were being mutated during initialization by wavesurfer.js, and when the React component re-rendered (especially in strict mode with double rendering), the same mutated plugin instances were passed to a new wavesurfer instance, causing errors.

Solution

Modified the useWavesurferInstance hook to:

1. Exclude plugins from deep dependency comparison - Created optionsWithoutPlugins that separates plugins from other options
2. Track plugin array reference separately - Added options.plugins directly to the useEffect dependency array, so the instance only recreates when the plugins array reference changes (not when individual plugins are mutated)
3. Pass plugins correctly - Spread optionsWithoutPlugins and explicitly pass plugins: options.plugins to ensure plugins are included

Key Benefits

• ✅ Plugins work correctly in React strict mode (double render)
• ✅ Plugin instances are not re-initialized on every render
• ✅ Users can memoize the plugins array with useMemo() to prevent unnecessary wavesurfer re-creation
• ✅ All existing tests pass
• ✅ Added comprehensive plugin test to verify the fix

Changes

• Modified src/index.tsx to handle plugins separately in dependency tracking
• Added test case for plugin re-render behavior
• Updated README.md with detailed plugin usage examples and memoization requirements (with bold warning that plugins must be memoized)

Testing

All tests pass including the new plugin test:

✓ should properly cleanup on unmount
✓ should render wavesurfer with basic options
✓ should render wavesurfer with events
✓ should handle plugins correctly and not break on re-render

The fix ensures plugin idempotency even when React strict mode causes double renders.

[katspaugh]

CI Status Update

The CI checks are showing failures, but these are due to GitHub Actions infrastructure/permissions issues, not code issues:

✅ Lint Check

Passes locally with no errors. CI failure is due to artifact upload permissions:

Error: Create Artifact Container failed: The artifact name eslint-v8-cache-key-state-Lint is not valid

✅ Tests Check

All tests pass (4/4 including the new plugin test). CI failure is due to missing checks: write permission:

Tests:       4 passed, 4 total
##[error]Missing checks: write permission

Local Verification

All checks pass locally:

• ✅ npm run lint - No errors
• ✅ npm test - 4/4 tests pass
• ✅ npm run build - Builds successfully

The code changes are ready for review. The CI failures are unrelated to this PR.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	63.89% (+11.03% 🔼)	46/72
🟡	Branches	63.64% (+27.27% 🔼)	14/22
🔴	Functions	56.25% (+4.64% 🔼)	18/32
🟢	Lines	100%	1/1

Test suite run success

4 tests passing in 1 suite.

Report generated by 🧪jest coverage report action from e199f76