- Move Interrupt and InterruptExecutor from `embassy` to `embassy-cortex-m`.
- Move Unborrow from `embassy` to `embassy-hal-common` (nothing in `embassy` requires it anymore)
- Move PeripheralMutex from `embassy-hal-common` to `embassy-cortex-m`.
Following the project's decision that "leak unsafe" APIs are not marked as "unsafe",
update PeripheralMutex to accept non-'static state without unsafe.
Fixes#801