feat: add Snow and Rain particle effect components

[mfazekas]

Summary

Implements <Snow /> and <Rain /> components that expose the experimental Mapbox Maps SDK v11.9+ precipitation particle effects to React Native. Follows the existing <Atmosphere /> pattern throughout.

• Code generator: registers snow and rain as singleton style layers, generates SnowLayerStyleProps / RainLayerStyleProps TypeScript types and native style setters
• iOS: RNMBXSnow / RNMBXRain Swift singleton layer implementations + Fabric component views
• Android: RNMBXSnow / RNMBXRain Kotlin implementations + ViewManagers, registered in RNMBXPackage
• TypeScript: Snow.tsx / Rain.tsx components exported from Mapbox.native.ts
• Example: new SnowAndRain example (V11) + Snow/Rain toggle buttons integrated into TerrainSkyAtmosphere
• SDK bump: Mapbox Maps iOS + Android 11.18.2 → 11.20.1
• measure-light warning: Rain logs a warning when used on styles without 3D lights and missing explicit color/opacity/vignetteColor

Screenshots

	iOS	Android
Snow
Rain

iOS Rain workaround

The Mapbox SDK's MapContentReconciler resets programmatically-applied Rain after isStyleRootLoaded fires (which can happen after tile/sprite loading completes, well after the initial styleLoaded event). Since the style JSON has no rain key, the reconciler resets it to nil. RNMBXRain.addToMap schedules an async re-apply to survive this reset. Snow does not exhibit the same behaviour.

To investigate the exact trigger: add a symbolic breakpoint in Xcode on MapboxMaps.StyleManager.setStyleRainForProperties with "Automatically continue after evaluating" + a backtrace action — the callstack will pinpoint what fires it.

Test plan

• yarn generate produces SnowLayerStyleProps / RainLayerStyleProps in src/utils/MapboxStyles.ts
• iOS build succeeds (Xcode, after pod install)
• Android build succeeds (./gradlew assembleDebug)
• Open TerrainSkyAtmosphere example → tap Snow → snowfall visible
• Tap Rain → rain visible and persists
• Tap Clear → effect removed; tap Rain again → rain reappears
• Open Snow & Rain (V11) example → same checks on a plain style