refactor: move docs engine into iroh-docs #8469

Job	Run time
Checking fmt	7s
cargo deny	29s
check_semver	1m 51s
Checking docs	1m 30s
clippy_check	2m 4s
Cross Build Only (armv7-linux-androideabi)	1m 2s
Cross Test (i686-unknown-linux-gnu)	2m 8s
Cross Build Only (aarch64-linux-android)	1m 0s
Cross Build Only (x86_64-unknown-freebsd)	1m 7s
Cross Build Only (x86_64-unknown-netbsd)	1m 10s
Minimal Supported Rust Version	1m 45s
Run network simulations/benchmarks	1m 4s
Build wasm32	28s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	1m 54s
CI Test Suite / Tests (ubuntu-latest, stable, all)	41s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	1s
CI Test Suite / Tests (ubuntu-latest, stable, none)	48s
CI Test Suite / Tests (ubuntu-latest, stable, default)	47s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	1m 54s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	47s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	2m 8s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	49s
	25m 34s

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