refactor: add `iroh_net::ConnManager` and use in `iroh_gossip::net` #8395

Job	Run time
check_semver	37s
Build wasm32	26s
cargo deny	28s
Checking docs	50s
Checking fmt	9s
clippy_check	48s
Cross compile (i686-unknown-linux-gnu)	50s
Cross compile (armv7-linux-androideabi)	52s
Minimal Supported Rust Version	50s
Cross compile (aarch64-linux-android)	53s
Run network simulations/benchmarks	53s
CI Test Suite / Tests (ubuntu-latest, stable, all)	50s
CI Test Suite / Tests (ubuntu-latest, stable, none)	1s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	51s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	38s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	1s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	1s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	51s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	40s
	11m 30s

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