iOS: Add map marker clustering

Description

Add marker clustering to the iOS map screen, similar to the Android implementation.

Context

Android now uses maps-compose-utils Clustering composable for map markers. iOS should implement equivalent functionality using the Google Maps iOS SDK clustering utilities.

Requirements

• Cluster markers when zoomed out
• Show individual markers with thumbnails when zoomed in
• Show cluster count badge
• Match Android behavior

Reference

• Android implementation: MapScreen.kt using Clustering composable
• SpotClusterItem implementing ClusterItem interface