feat: implementation of diff

[kikoso]

The following PR implements the diff option to add, remove and update items on a Cluster. It also provides a sample on how to implement it on the app, including modifying the ClusterItem extended object to add the equals() method. It provides a Custom Renderer as a sample, as well.

Summary of changes:

• Implementation of a diff() method in the ClusterManager, to pass at once all the required ClusterItems to be removed.
• Sample implementing equals in the demo, to determine how the ClusterItems are rendered unique.
• New Cluster to render multiple items.
• New demo, to showcase how to use it

This is a diagram that showcases the relationship between the main components in the Clustering.

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Code Coverage

Overall Project	34.83% -8.95%	🍏
Files changed	0%	❌

File	Coverage
ClusterManager.java	0% -10.21%	❌
ClusterRendererMultipleItems.java	0%	❌
DefaultClusterRenderer.java	0% -2%	❌