refactor: add `iroh_net::ConnManager` and use in `iroh_gossip::net` #8401

Job	Run time
check_semver	5m 11s
Build wasm32	29s
Checking fmt	8s
Checking docs	1m 51s
cargo deny	31s
clippy_check	3m 10s
Cross compile (i686-unknown-linux-gnu)	2m 30s
Minimal Supported Rust Version	2m 3s
Cross compile (armv7-linux-androideabi)	1m 2s
Cross compile (aarch64-linux-android)	1m 0s
Run network simulations/benchmarks	7m 51s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	3m 49s
CI Test Suite / Tests (ubuntu-latest, stable, all)	3m 18s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	3m 48s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	3m 47s
CI Test Suite / Tests (ubuntu-latest, stable, none)	3m 5s
CI Test Suite / Tests (ubuntu-latest, stable, default)	4m 30s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	3m 51s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	3m 2s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	3m 41s
	58m 37s

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