The `interrupt` package previously tried to be drop-in compatible with the
`interrupt` package from PACs. THis meant that there was both a PAC-style enum
value `UARTE0` and an embassy-style owned `UARTE0Interrupt` type. This made
things VERY confusing.
This drops compatibility with the PAC, improving the names for embassy interrupts.
- It's no longer possible to call run() reentrantly from within a task (soundness issue)
- it's now possible to spawn Send tasks across threads (SendSpawner, #37)
