TimerHandle callback fixes/improvements

[stephenhensley]

This accomplishes a few related things:

• Implements the user-callback for the rest of the supported, generic TIM instances (TIM2, TIM3, TIM4)
• Fixes bug where DAC DMA/Callback usage would crash due to null Impl::Config object in internal hardware init
• Adds example of using the new TimerHandle::PeriodElapsedCallback

[github-actions[bot]]

Unit Test Results

    1 files    16 suites   0s :stopwatch: 147 tests 147 :heavy_check_mark: 0 :zzz: 0 :x:

Results for commit f26079f7.

:recycle: This comment has been updated with latest results.

[stephenhensley]

Tested:

• Daisy Patch SM Envelope example (uses TIM6 based DAC callback)
• new TIM5 based callback example
• Tested modified example using TIM4 peripheral
• Tested modified example using TIM3 peripheral
• Tested modified example using TIM2 peripheral*

Re. TIM2

Opened new issue (#524) to describe weirdness with attempting DeInit prior to Init.

For clarity, when using TIM2 (which is internally used by the System class), I had to Init the TIM2 peripheral, then DeInit before initializing again to have a clean state to start a callback from.

This particular use is outside the scope of this PR.