Fix ConcurrentModificationException in LiveMetricsVerifier by using CopyOnWriteArrayList

[Copilot]

This PR fixes a sporadic test failure where LiveMetricsVerifier.getRequestCount() throws a ConcurrentModificationException when iterating over the points ArrayList while another thread is modifying it.

Problem

The issue manifests as:

java.util.ConcurrentModificationException
    at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013)
    at java.base/java.util.ArrayList$Itr.next(ArrayList.java:967)
    at com.microsoft.applicationinsights.smoketest.fakeingestion.LiveMetricsVerifier.getRequestCount(LiveMetricsVerifier.java:46)

Root Cause:

• The points field is an ArrayList<MonitoringDataPoint> accessed from multiple threads
• One thread calls apply() to add elements while another thread iterates in getRequestCount(), getExceptionCount(), etc.
• ArrayList is not thread-safe, causing the concurrent modification exception

Solution

Replace ArrayList with CopyOnWriteArrayList for thread-safe iteration in this read-heavy workload.

Changes made:

• Changed ArrayList<MonitoringDataPoint> to CopyOnWriteArrayList<MonitoringDataPoint> in the points field
• Updated imports to include java.util.concurrent.CopyOnWriteArrayList
• Removed unused ArrayList import

Why CopyOnWriteArrayList:

• Thread-safe for concurrent read/write operations
• Optimal for read-heavy workloads (which matches the usage pattern in tests)
• Provides consistent iteration without ConcurrentModificationException
• Minimal performance impact for the test framework context

This change ensures that all methods like getRequestCount(), getExceptionCount(), getTraceCount(), etc. can safely iterate over the list while other threads are adding new monitoring data points.

Fixes #4327.

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