Fix 615 fixed waveform

[gitpsii]

Description

add_baseline_and_extend_tailpreviously returned the waveform signal as a regularVector`, even though the waveform length is required to remain fixed for DAQ waveform processing.

This change wraps the allocated signal in a SizedVector with total_waveform_length as its static size.

Testing

Added tests to verify that the returned signal is a SizedVector and has the expected length.

Fixes #615

[fhagemann]

Thanks for the contribution:
I’ll leave the decision to @oschulz, who might have some opinion about using ArraysOfArrays here.

[oschulz]

total_waveform_length is not known at compile time and can be quite large, I don't think we want to type-parameterize based on it.

[gitpsii]

Thanks, that makes sense. I see that SizedVector{total_waveform_length would type-parameterize on a runtime value and could be problematic for large waveform lengths. What fixed-length array type/approach would you recommend for this function?

[oschulz]

We could look into using FixedSizeArrays.