Add UDS support

[yoshuawuyts]

Refs

• https://github.com/haraldh/rust_uds_windows
• https://github.com/Azure/mio-uds-windows

Explainer

Two "extension" traits, UnixListenerExt and UnixStreamExt, and their implementations, were adapted from their TCP counterparts in the miow library.

Unix Domain Sockets have recently become available on Windows. This feels like it's closely enough related to miow that we could provide some of the conveniences that currently exist in other crates here as well.