Add regularized regression methods and improve some tests

[danielnachun]

This PR adds support for several new regression methods to match what is available in the mr.ash paper.

I have also worked to maximize test coverage for the fine mapping, TWAS and regularized regression code.

I had to disable the tests and code that rely on summary-based methods for qgg because these are missing from the current CRAN version of qgg. It seems the authors are actively updating their code over the last few days, so they may be preparing a new release. If one doesn't come out soon, we should contact them.

[codecov]

Codecov Report

❌ Patch coverage is 95.34884% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.70%. Comparing base (0517999) to head (69659bd).
⚠️ Report is 1026 commits behind head on main.

Files with missing lines	Patch %	Lines
R/regularized_regression.R	95.12%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #467       +/-   ##
===========================================
+ Coverage   27.48%   76.70%   +49.21%     
===========================================
  Files          32       41        +9     
  Lines        4377     7941     +3564     
===========================================
+ Hits         1203     6091     +4888     
+ Misses       3174     1850     -1324     

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