test(r/demo/tests): add filetest for PrevRealm #7844

Job	Run time
Run Main (autocounterd) / Go Linter / lint	25s
Run Main (autocounterd) / Go Build / generated	7s
Run Main (autocounterd) / Go Test / test	36s
Run Main (genproto) / Go Build / generated	7s
Run Main (genproto) / Go Linter / lint	39s
Run Main (genproto) / Go Test / test	44s
Run Main (genstd) / Go Build / generated	5s
Run Main (genstd) / Go Linter / lint	18s
Run Main (genstd) / Go Test / test	28s
Run Main (goscan) / Go Build / generated	10s
Run Main (goscan) / Go Linter / lint	24s
Run Main (goscan) / Go Test / test	21s
Run Main (docker-integration) / Go Build / generated	8s
Run Main (docker-integration) / Go Linter / lint	5s
Run Main (docker-integration) / Go Test / test	19s
Run Main (logos) / Go Build / generated	7s
Run Main (logos) / Go Linter / lint	25s
Run Main (logos) / Go Test / test	45s
Run Main (loop) / Go Build / generated	12s
Run Main (loop) / Go Linter / lint	33s
Run Main (loop) / Go Test / test	40s
	7m 38s

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