feat: init PgElection with candidate registration (#5209)

* feat: init PgElection

fix: release advisory lock

fix: handle duplicate keys

chore: update comments

fix: unlock if acquired the lock

chore: add TODO and avoid unwrap

refactor: check both lock and expire time, add more comments

chore: fmt

fix: deal with multiple edge cases

feat: init PgElection with candidate registration

chore: fmt

chore: remove

* test: add unit test for pg candidate registration

* test: add unit test for pg candidate registration

* chore: update pg env

* chore: make ci happy

* fix: spawn a background connection thread

* chore: typo

* fix: shadow the election client for now

* fix: fix ci

* chore: readability

* chore: follow review comments

* refactor: use kvbackend for pg election

* chore: rename

* chore: make clippy happy

* refactor: use pg server time instead of local ones

* chore: typo

* chore: rename infancy to leader_infancy for clarification

* chore: clean up

* chore: follow review comments

* chore: follow review comments

* ci: unit test should test all features

* ci: fix

* ci: just test pg

.github/workflows/develop.yml

@@ -697,7 +697,7 @@ jobs:
         working-directory: tests-integration/fixtures/postgres
         run: docker compose -f docker-compose-standalone.yml up -d --wait
       - name: Run nextest cases
-        run: cargo llvm-cov nextest --workspace --lcov --output-path lcov.info -F pyo3_backend -F dashboard
+        run: cargo llvm-cov nextest --workspace --lcov --output-path lcov.info -F pyo3_backend -F dashboard -F pg_kvbackend
         env:
           CARGO_BUILD_RUSTFLAGS: "-C link-arg=-fuse-ld=lld"
           RUST_BACKTRACE: 1