Enhance react-native-barometer for v2.1

[dpyeates]

Summary

Implements the review recommendations as v2.1.0: safer Turbo Module loading, richer API, TypeScript packaging, restored example app, CI, and docs.

P0 / correctness

• Soft-fail when the native module is missing (isSupported() → false, watch() → -1) instead of crashing AppRegistry
• Surface sensor failures via onBarometerError / optional watch error callback
• Replace broken empty example submodule with an in-repo RN 0.86 New Architecture example

API / DX

• useBarometer() hook with automatic cleanup
• setSmoothing(alpha), setAltitudeReference(metres), resetRelativeAltitude()
• Export getAltitude / pressureFromAltitude
• Payload accuracy field (Android; -1 on iOS)
• Monotonic watch IDs
• TypeScript source → lib/ with package exports

Tooling / docs

• Peer dependency widened to react-native >= 0.84
• GitHub Actions CI (typecheck, unit tests, example install)
• README, CHANGELOG.md, MIGRATION.md (including Expo Dev Client notes)
• CI test script uses explicit file paths so Node 20 and 22 both pass

Test plan

• npm test (validation + watchManager)
• npm run typecheck
• Example npm ci succeeds
• CI green on Node 20 + 22 (after glob fix)
• Manual: run example on a device/simulator with a barometer and verify hook + calibration controls