embassy-nrf: Timer HAL broken for extended timers (TIMER3/TIMER4)

[peter9477]

The embassy-nrf timer.rs implementation has an impl_timer! macro that allows defining "extended" timers (which is used for TIMER3 and TIMER4 on chips where those are supported). This creates a constant CCS equal to 4 or 6, which is used in the Timer::new() to initialize the CC registers. This will panic at run time when TIMER3 or TIMER4 are used to create a Timer, because the impl_timer! macro involves only pac::timer0, which has only 4 CC registers.

As noted in the discussion below https://matrix.to/#/!YoLPkieCYHGzdjUhOK:matrix.org/$dC6N7X1MOSACQwlS0GI9wZsCKI1HS-yGsHlTPTAAEt8?via=matrix.org&via=tchncs.de&via=grusbv.com this will need to reference pac::timer3, possibly via a regs_ext() implementation in the trait (as suggested by @Dirbaio).