feat: expose map zoom limits

[arpitagarwal1301]

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Fixes #472 🦕

Summary

• expose minZoomLevel and maxZoomLevel as read-only nullable properties on CameraPositionState
• delegate both values to the currently bound GoogleMap, returning null while unbound
• add focused instrumentation coverage for the unbound and map-loaded states

Testing

• ./gradlew :maps-compose:compileDebugKotlin :maps-app:compileDebugAndroidTestKotlin --stacktrace --no-daemon
• ./gradlew build jacocoTestReport :maps-app:validateDebugScreenshotTest -x :maps-app:generateDebugScreenshotTestConfig -x :maps-app:generateReleaseScreenshotTestConfig --stacktrace --no-daemon
• git diff --check

The API-key-dependent connected instrumentation test compiled locally but was not run because the checkout has only the placeholder key; the repository instrumentation workflow injects its Maps API secret.

AI disclosure

This focused change was prepared and independently reviewed with AI assistance.