add statime-embassy-net

[jordens]

This adds a statime ordinary-clock runner for embassy plus an example.
It uses the shared fixed-wander servo (#872) and Embassy's generic network clock interface (embassy-rs/embassy#6802). That way e.g. an ESP CPU implementing the embassy clock trait can directly use this runner.

This also keeps the library outside Statime's workspace and the STM32H743 application in
its own standalone workspace. That way (like for the statime-stm32 example) board dependencies, target configuration, linker script, lockfile, and crate patches are contained.

Depends on the Embassy network-clock PR embassy-rs/embassy#6802

Stacks on top of #871 and #872

Close #845

I know I'm targetting a potentially dead horse but it's the most convenient approach currently. Happy to retarget later to whatever shape ntpd-rs ultimately assumes.

[davidv1992]

Apologies for the delay in looking at this. I'm not sure yet whether we are going to want this once the merger with ntpd-rs has gone through. This adds quite a bit of hardware-specific code that isn't really the core focus of the project, and we might just not have the bandwidth to do maintenance on this.

[jordens]

Sure. But note that this is very much not hardware specific. It supports all of the STM32 ETH hardware that has PTP (silicon v1 and v2) plus any other future implementation of that ptp-driver trait that may come up (there is the esp family that just needs some glue code).
The example is necessarily hardware specific.