Added two SiN PCell to Beta Library

[Hang-Bobby-Zou]

• Added a slot_SiN.py PCell file for straight slot SiN waveguide since there is no option for SiN in the "path to waveguide" function. THIS IS ONLY TEMPORARY. Will raise issue and added the option once we know the default values from the openEBL-2024-10-SiN run
• Added a strip_to_slot_SiN.py PCell that allows tapers from a strip/slot with any width/slot width of your choice. Also added functionality for adiabatic taper to avoid any abrupt changes at the tip.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.01980% with 2 lines in your changes missing coverage. Please review.

Project coverage is 73.80%. Comparing base (d964c34) to head (b405184).

Files with missing lines	Patch %	Lines
...ayout/EBeam/pymacros/pcells_EBeam_Beta/slot_SiN.py	97.61%	1 Missing ⚠️
...am/pymacros/pcells_EBeam_Beta/strip_to_slot_SiN.py	98.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #309      +/-   ##
==========================================
+ Coverage   73.60%   73.80%   +0.20%     
==========================================
  Files          94       96       +2     
  Lines       11682    11783     +101     
==========================================
+ Hits         8598     8697      +99     
- Misses       3084     3086       +2     

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