Analytical method for regular RT structures and Lambertian scattering approximation

[phoebe-p]

• Speed improvements for all ray-tracing calculations, by using numba jit (just-in-time) compilation of heavily-used
  functions, and more efficient lookup of TMM values for integrated ray-tracing/TMM calculations.
• New analytical method for ray-tracing, which is much faster than full ray-tracing and can be used with full
  accuracy for surfaces where the number of ray interactions is known exactly in advance (e.g. upright pyramids with
  opening angles between 45 and 54 degrees). Note that the calculation of absorption profiles in interface layers
  is not yet implemented for this method (though this is on the roadmap, as there is no fundamental reason this
  cannot be done). Absorption in bulk layers is calculated as usual if the analytical method is used. This option
  can be toggled on per surface in an rt_structure object.
• Phong scattering: a new option for the ray-tracer, which allows additional non-specular scattering. The continuum
  between perfectly specular and Lambertian scattering can be controlled with the Phong exponent.
• Rigorous treatment of polarization in ray-tracing (no changes to treatment of polarization in TMM and RCWA calculations).
• Option to set a maximum number of bulk passes for the ray-tracer using the maximum_passes option
• More detailed output from ray-tracing calculations, and re-organization of returned data.
• Move to uv for install in GitHub actions instead of pip (faster)
• Schedule weekly test run on GitHub actions
• fix issues with examples in documentation
• new examples for new functionality
• lens_hyperhemisphere_rt parallelised over angles
• faster matrix multiplication for ARRM using einsum (thanks to Johnson Wong @arsonwong)
• default number of lookuptable angles changed from 300 to 200
• remove ability to set options.wavelengths (plural) instead of options.wavelength (next major version release deprecation)
• fix issue in TMM with zero thickness incoherent layers
• move to state (options.option) rather than dictionary (options["option"]) notation in multiple files
• new process_pol function to process strings or list into (s, p) format
• new tests for new functionality

[codecov]

Codecov Report

Attention: Patch coverage is 95.86592% with 37 lines in your changes missing coverage. Please review.

Project coverage is 93.65%. Comparing base (fd08085) to head (c692277).

Files with missing lines	Patch %	Lines
rayflare/ray_tracing/rt_common.py	95.04%	16 Missing ⚠️
rayflare/ray_tracing/rt_matrix.py	96.00%	11 Missing ⚠️
rayflare/ray_tracing/analytical_rt.py	96.49%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            devel      #68      +/-   ##
==========================================
+ Coverage   92.70%   93.65%   +0.95%     
==========================================
  Files          20       23       +3     
  Lines        3057     3737     +680     
==========================================
+ Hits         2834     3500     +666     
- Misses        223      237      +14     

Flag	Coverage Δ
	93.65% <95.86%> (?)

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