feat: let connection pool watch for connection close #533

Job	Run time
Cross Test (i686-unknown-linux-gnu)	3m 20s
Cross Build Only (x86_64-unknown-freebsd)	51s
Android Build Only (armv7-linux-androideabi)	1m 11s
Android Build Only (aarch64-linux-android)	2m 24s
check_semver	1m 16s
clippy_check	1m 18s
Checking fmt	26s
Checking docs	1m 9s
cargo deny	27s
Minimal Supported Rust Version	1m 6s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	2m 6s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	2m 4s
CI Test Suite / Tests (ubuntu-latest, stable, all)	1m 24s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	1m 39s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	2m 7s
codespell	6s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	1m 42s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	1m 37s
CI Test Suite / Tests (ubuntu-latest, stable, none)	1m 24s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1m 20s
	28m 57s

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