Add a function to generate arbitrary waveform

[picarro-yren]

This PR adds an arb_func in PulseAtoms to allow users generating arbitrary waveforms.

PulseAtoms only contains ramp and sine functions, but in real experiments more complicated waveforms are needed. For example, generating a waveform that contains 2 sine waves with different frequencies.

A unit test is also added for testing this new feature

[codecov-commenter]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (7cf96c8) 82.30% compared to head (b4c951b) 82.33%.

Files	Patch %	Lines
broadbean/broadbean.py	63.63%	8 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #779      +/-   ##
==========================================
+ Coverage   82.30%   82.33%   +0.03%     
==========================================
  Files          17       17              
  Lines        2441     2457      +16     
==========================================
+ Hits         2009     2023      +14     
- Misses        432      434       +2     

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