Type-safety and import conflict in google_maps_cluster_manager

[QuangNH0606]

Fix: Type-safety and import conflict in google_maps_cluster_manager

Summary

This Pull Request fixes a runtime error in the google_maps_cluster_manager package caused by the usage of untyped cluster variables and ambiguous imports between cluster.dart and cluster_manager.dart.

The original code caused analyzer issues due to implicit Object? usage and type inference failures when accessing cluster.location, cluster.count, or cluster.isMultiple.

Related Issues

• No official issue referenced, but this resolves a common runtime crash when using the package with Flutter 3.x and Dart null-safety.
• Also addresses [Flutter analyzer error]: "The method 'location' isn't defined for the type 'Object?'".

Changes Introduced

• ✅ Added generic typing to _basicMarkerBuilder<T> method.
• ✅ Aliased imports of cluster.dart and cluster_manager.dart to avoid conflict.
• ✅ Explicitly cast cluster to Cluster<T> before accessing typed members (location, isMultiple, count).
• ✅ Ensured compatibility with Dart strong mode and current Flutter SDK.

Before (Problematic code)

final latLng = cluster.location; // ❌ Error: Object? has no method 'location'