feat: New parametrizations for external shear and point mass

[ConnorStoneAstro]

No description provided.

[ConnorStoneAstro]

Closes #196

[codecov]

Codecov Report

Attention: Patch coverage is 95.96774% with 5 lines in your changes missing coverage. Please review.

Project coverage is 92.16%. Comparing base (ea277ed) to head (3ea22ad).
Report is 14 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/caustics/lenses/point.py	94.44%	2 Missing ⚠️
src/caustics/lenses/sie.py	94.28%	2 Missing ⚠️
src/caustics/lenses/external_shear.py	97.67%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #304      +/-   ##
==========================================
+ Coverage   91.92%   92.16%   +0.23%     
==========================================
  Files          55       55              
  Lines        2279     2399     +120     
==========================================
+ Hits         2095     2211     +116     
- Misses        184      188       +4     

Flag	Coverage Δ
unittests	92.16% <95.96%> (+0.23%)	⬆️

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[ConnorStoneAstro]

Now also new parametrization for SIE

[mjyb16]

Very slick! I will be testing this out in real life on real data quite soon, let's merge it and patch later if needed.