refactor!: merge admin and standard clients, merge sync and async integration tests, use test fixtures for setup and teardown, add missing docstrings. vec-466 vec-344 vec-388 vec-481 vec-373

refactor!: merge admin and standard clients, merge sync and async integration tests, use test fixtures for setup and teardown, add missing docstrings. vec-466 vec-344 vec-388 vec-481 vec-373 #398