Function _trySwitchByTiles

_trySwitchByTiles(
    map: SourceReaderLike,
    previous: BasemapDefinition | null | undefined,
    next: BasemapDefinition,
    onWarn: (message: string, error: unknown) => void,
): boolean
Mutates the live raster source's tile URLs instead of destroying and rebuilding it.

Only when the two basemaps differ by their tiles alone (_canSwitchByTiles): any other change is baked into the source at creation and would be silently kept. Returns false whenever the mutation cannot be trusted, so the caller falls back to the remove + re-add path — which stays the general case, not a degraded one.
Parameters
- map: SourceReaderLike
  Anything exposing getSource; the live raster source is read off it.
- previous: BasemapDefinition | null | undefined
  The basemap currently applied, or null/undefined at boot — in which case there is nothing to mutate and the call returns false.
- next: BasemapDefinition
  The basemap being switched to; its tiles are the ones written.
- onWarn: (message: string, error: unknown) => void
  Reports a failed mutation; the caller then rebuilds.
Returns boolean
true when the tiles were mutated in place.
- Defined in src/kernel/basemaps/basemaps-apply.ts:159