KAFKA-20965: Remove hamcrest from org.apache.kafka.streams.state.internals.metrics package

[korih]

Migrated hamcrest to junit

[Copilot]

Pull request overview

This PR updates Kafka Streams state-store metrics unit tests in org.apache.kafka.streams.state.internals.metrics to eliminate Hamcrest usage by switching assertions to JUnit Jupiter.

Changes:

• Replaced assertThat(..., is(...)) with Assertions.assertEquals(...) for object and message comparisons.
• Replaced notNullValue() checks with Assertions.assertNotNull(...) where applicable.
• Removed Hamcrest static imports from the affected test classes.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
streams/src/test/java/org/apache/kafka/streams/state/internals/metrics/StateStoreMetricsTest.java	Switches Hamcrest assertThat/is to JUnit assertEquals for sensor verification.
streams/src/test/java/org/apache/kafka/streams/state/internals/metrics/RocksDBMetricsTest.java	Replaces Hamcrest equality assertion with JUnit assertEquals.
streams/src/test/java/org/apache/kafka/streams/state/internals/metrics/RocksDBMetricsRecorderTest.java	Converts multiple Hamcrest assertions (including exception message checks) to JUnit assertEquals.
streams/src/test/java/org/apache/kafka/streams/state/internals/metrics/RocksDBMetricsRecorderGaugesTest.java	Replaces Hamcrest null/equality assertions with assertNotNull and assertEquals.
streams/src/test/java/org/apache/kafka/streams/state/internals/metrics/NamedCacheMetricsTest.java	Updates Hamcrest sensor equality assertion to JUnit assertEquals.

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