Make CTimerPwmPeriodChannel::new (and others) compile-time validated for const arguments

[bscoggins-msft]

Currently, CTimerPwmPeriodChannel::new returns a Result and can fail at runtime, requiring .expect("...") calls even when the arguments are compile-time constants that are known to be valid.

Requested improvement:
Either:

1. Make the constructor const fn with compile-time validation - Use const { assert!() } blocks to validate arguments at compile time, making invalid arguments a compiler error rather than runtime panic
2. Provide a separate const fn new_const() variant that only accepts const arguments and validates them at compile time