Add unit test for block-builder #9531

Job	Run time
Build	1m 53s
Benchmark	7m 16s
Lint	48s
Run integration tests (test-e2e)	29m 32s
Run Unit Tests (test-with-cover-pkg)	3m 15s
Run integration tests (test-integration-poller)	10m 2s
Run Unit Tests (test-with-cover-tempodb)	3m 30s
Vendor check	1m 28s
Run integration tests (test-e2e-deployments)	29m 23s
Run integration tests (test-e2e-serverless)	7m 17s
Run Unit Tests (test-with-cover-tempodb-wal)	3m 29s
Build technical documentation	21s
Run Unit Tests (test-with-cover-others)	3m 30s
Check jsonnet & tempo-mixin	51s
	1h 42m 35s

Provide feedback