[google_maps_flutter] Improved perfomance of clusterization

[OlehSv]

Google Maps implementation for flutter web is invoking rendering after each added marker to cluster. It is extremely non optimal, as result app is freezing for some time in case of significant number of markers (200+, but it is more obvious for 1k+) especially if they are using images instead of default icon.

As fix I am proposing to utilize method addItems of JS implementation instead of addMarker and render only as batch of markers are added.

I have tested new implementation with 3k markers and before it was freezed for 15-30 seconds, now it works without any freeze at all.

Fixes #179456

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[gemini-code-assist]

Code Review

This pull request introduces a significant performance improvement for marker clustering on the web by batching add and remove operations. Instead of re-rendering after each individual marker change, the changes are now grouped by cluster manager and applied in a single batch, followed by a single render call. This is achieved by introducing addItems and removeItems methods in ClusterManagersController and updating MarkersController to use them. The code in MarkersController has been refactored to support this, with _addMarker being split into a new _createMarker method for better code reuse. The changes look solid and directly address the performance issue described.

[OlehSv]

@mdebbar Could you review please? It is quite safe PR, it has minimal changes to specific feature

[mdebbar]

I'm not familiar with Google Maps' clustering APIs, but the code in this PR looks good to me overall.

/gemini review

[OlehSv]

@mdebbar Resolved comment

[mdebbar]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a significant performance improvement for marker clustering on the web by batching the addition and removal of markers. Instead of re-rendering after each individual marker operation, the changes leverage the addMarkers and removeMarkers methods of the underlying JavaScript library to process markers in bulk, triggering a single render per batch. This is an excellent optimization that will prevent UI freezes when dealing with a large number of markers.

The implementation is solid, with corresponding changes in the MarkersController to group markers by cluster and use the new batching methods. A new integration test has been added to verify that clustering events are fired only once per batch, confirming the effectiveness of the change. I have one minor suggestion to improve efficiency in the removeMarkers method.

[mdebbar]

LGTM, thanks for the improvements!

[OlehSv]

@mdebbar All tests have passed. What do I need to do to merge PR?

[OlehSv]

@stuartmorgan-g, I’ve updated the code. It should address all your comments

[stuartmorgan-g]

One minor question, but LGTM for landing once the conflicts are resolved. (Please ping me when that's done so I know it's ready to land.)

[OlehSv]

@stuartmorgan-g I have done conflicts resolving, but they was significant (whole class of markers was added) so make sense to repeat review.

[stuartmorgan-g]

Still LGTM, thanks!