refactor: Replace connection pool #523

Job	Run time
Cross Build Only (x86_64-unknown-freebsd)	50s
Checking fmt	31s
Checking docs	1m 9s
Android Build Only (armv7-linux-androideabi)	1m 21s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	2m 1s
Cross Test (i686-unknown-linux-gnu)	4m 26s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	2m 3s
Minimal Supported Rust Version	1m 18s
Android Build Only (aarch64-linux-android)	1m 17s
codespell	7s
clippy_check	1m 44s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	1m 45s
cargo deny	30s
CI Test Suite / Tests (ubuntu-latest, stable, all)	1m 48s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	2m 5s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1m 27s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	1m 37s
check_semver	1m 22s
CI Test Suite / Tests (ubuntu-latest, stable, none)	1m 27s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	1m 35s
	30m 23s

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