libudev replacement

[Ravenslofty]

Sharing a libudev context between threads is not safe (in rust terms a context is !Send), even when guarded by a mutex. This means that a USB context that depends on libudev must also be !Send. As a result, a Rust library needs to be created to talk to udev directly without using libudev.

[Ravenslofty]

So, having done some investigation, I think the safest approach is to make the whole library !Send and !Sync.

[kevinmehall]

Apparently the udev context isn't even necessary in modern versions of libudev: dcuddeback/libudev-rs#22

The documentation is outdated/unclear, but it indeed appears to not do anything: https://github.com/systemd/systemd/blob/24e4b4a199edd7fa743b39a36aa14d312fb94be5/src/libudev/libudev.c#L27