[google_maps_flutter_android] Batch clustered marker operations (#10940)

Note: this PR attempts to use the same strategy from the Google Maps Flutter Web PR https://github.com/flutter/packages/pull/10562 and apply it to Google Maps Flutter Android.

## Summary
- Adds batch `addItems()` and `removeItems()` methods to `ClusterManagersController`
- Refactors `MarkersController` to batch add/remove/change operations for clustered markers
- Reduces redundant re-clustering calls when multiple markers are added/removed/changed at once

This improves performance when working with large numbers of clustered markers by calling `ClusterManager.cluster()` once per cluster manager instead of once per marker.

## Test plan
- Added unit tests for batch add/remove operations
- Added unit test for batch cluster manager changes
- Existing tests pass

Addresses https://github.com/flutter/flutter/issues/170573

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