Implement multiround benchmarking & enhance `LLMService` interfaces #74

Job	Run time
build-and-test (ubuntu-latest, 4.14)	11m 26s
build-and-test (macos-latest, 4.14)	13m 51s
Start a CI debug session if build or test fail (ubuntu-latest, 4.14)	2s
	25m 19s

Provide feedback