Add a simulated network

[dhruvl]

Adds an in-memory network to the simulation, so real asyncio networking code runs unmodified on SimLoop with seeded, replayable faults:

• host registry with per-host task pinning, addresses resolved inside the sim
• datagram endpoints over a packet core with seeded drop / duplication / reordering / latency per link
• stream connections behind the standard asyncio streams API (open_connection / start_server), including backpressure and half-close
• network partitions that hold traffic until healed, and host crash injection that tears down the crashed host's open connections without emitting resets
• close_clients / abort_clients on simulated servers, matching 3.13 stdlib semantics
• replay stability proven for network workloads: byte-identical traces across 100 reruns per seed and across processes under varying PYTHONHASHSEED
• docs: the simulated network and the updated supported-API page

82 tests green on 3.12 and 3.13, zero warnings, mypy strict clean on both.