* feat: txn for pg kv backend
* chore: clippy
* fix: txn uses one client
* test: clean up and txn test
* test: clean up
* test: change lock_id to avoid conflict in test
* test: use different prefix in pg election test
* fix(test): just a fix
* test: aggregate multiple test to avoid concurrency problem
* test: use uuid instead of rng
* perf: batch cmp in txn
* perf: batch same op in txn