feat: Migrate java-test-helpers to java-core. (#90) #66

Job	Run time
release-please	24s
release-server-sdk-otel	0s
release-sdk-internal	0s
release-sdk-common	0s
release-test-helpers	0s
release-server-sdk	0s
release-server-sdk-redis-store	0s
release-please	16s
release-sdk-internal	-1s
release-test-helpers	-1s
release-server-sdk-redis-store	-1s
release-server-sdk-otel	-1s
release-sdk-common	-1s
release-server-sdk	-1s
	34s

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