Add test for MessageStack.peek() skipping removed messages

This test verifies that MessageStack.peek() correctly iterates past messages that have been marked for removal and returns the next available message. It also confirms that the skipped messages are purged from the underlying heap during this process.


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Original Change: ag/34942155
Test: ATP tests passed http://go/forrest-run/L10600030017425301
Bug: 431235865
Flag: TEST_ONLY



Change-Id: Ideb5956d3cba78e25116ffe46bee3da0471cb780