refactor: extract `ProtocolHandler` impl into here #7

Job	Run time
cargo deny	34s
Android Build Only (aarch64-linux-android)	1m 11s
Checking docs	1m 8s
Android Build Only (armv7-linux-androideabi)	1m 6s
Checking fmt	25s
check_semver	23s
clippy_check	1m 53s
codespell	3s
Cross Build Only (x86_64-unknown-freebsd)	42s
Cross Test (i686-unknown-linux-gnu)	59s
Minimal Supported Rust Version	1m 26s
CI Test Suite / Tests (ubuntu-latest, stable, all)	1m 11s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	1m 33s
CI Test Suite / Tests (ubuntu-latest, stable, none)	26s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1m 3s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	1m 0s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	51s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	1m 36s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	30s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	1m 14s
	19m 14s

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