fix: Ensure we reset state when changing sources in MultiCOGLayer

[kylebarron]

For #142, related to #147

Previously, switching sources rendered old data. Now, we correctly render the latest data whenever we switch sources.

Screen.Recording.2026-04-10.at.3.25.28.PM.mov

Root cause: _parseAllSources() is async, but renderLayers() runs synchronously after updateState. The new TileLayer was created with new props-derived sourceUrls in its id/updateTriggers, causing tile re-fetches. But _getTileData read band data from this.state.sources which still held the old source map. Tiles were cached under the new TileLayer with wrong band names, and when _parseAllSources finally completed, the cached tiles persisted — causing _renderSubLayers to return null (required bands missing).