feat: let connection pool watch for connection close #539

Job	Run time
Android Build Only (aarch64-linux-android)	1m 10s
Android Build Only (armv7-linux-androideabi)	1m 11s
check_semver	1m 29s
Checking fmt	39s
clippy_check	1m 29s
Minimal Supported Rust Version	1m 2s
Cross Build Only (x86_64-unknown-freebsd)	50s
Cross Test (i686-unknown-linux-gnu)	5m 37s
cargo deny	26s
Checking docs	53s
codespell	5s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	2m 7s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	2m 7s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	2m 13s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1m 37s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	1m 43s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	1m 40s
CI Test Suite / Tests (ubuntu-latest, stable, none)	1m 32s
CI Test Suite / Tests (ubuntu-latest, stable, all)	1m 42s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	1m 44s
	31m 16s

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