test: add concurrent dump/checkPoint stress test for Profiler

[chhil]

Summary

Add a multi-threaded stress test that verifies Profiler.dump() and Profiler.checkPoint() can be called concurrently without triggering ConcurrentModificationException.

Test Details

The test spawns 4 writer threads (2000 checkpoints each) alongside a single dumper thread (2000 dumps), all starting simultaneously via CountDownLatch to maximize the chance of catching race conditions.

Test strategy

• Multiple threads call checkPoint() with unique event names, modifying the shared events map
• A separate thread continuously calls dump(), which iterates over the same map
• Thread.yield() calls every 10 iterations increase lock contention between threads
• Any exception (including ConcurrentModificationException) is captured via an AtomicBoolean flag

Motivation

This test validates the fix from PR #715 (Avoid concurrent modification while dumping Profiler) by simulating the real-world scenario where one thread is logging/dumping profiler results while other threads are simultaneously recording checkpoints.

Test Plan

• Test compiles and passes locally
• CI checks pass

Assisted-by: Hermes Agent:qwen36