implement time delay likelihood + other fixes

[ahuang314]

1. Modify the lens equation solver default arguments to be the same as lenstronomy
2. Fix the LensModel initialization to include ddt scaling and z_source/z_source_convention initialization (matching lenstronomy behavior)
3. Implement time delay likelihood

[codecov]

Codecov Report

❌ Patch coverage is 95.32710% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.91%. Comparing base (23a4f5c) to head (8830c03).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...nomy/Sampling/Likelihoods/time_delay_likelihood.py	94.73%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
- Coverage   99.98%   99.91%   -0.07%     
==========================================
  Files          80       81       +1     
  Lines        7330     7437     +107     
==========================================
+ Hits         7329     7431     +102     
- Misses          1        6       +5     

Files with missing lines	Coverage Δ
...axtronomy/LensModel/Solver/lens_equation_solver.py	99.47% <ø> (ø)
jaxtronomy/LensModel/lens_model.py	100.00% <100.00%> (ø)
jaxtronomy/PointSource/point_source.py	100.00% <100.00%> (ø)
...nomy/Sampling/Likelihoods/time_delay_likelihood.py	94.73% <94.73%> (ø)

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[sibirrer]

Thank you @ahuang314! I have one comment about a for-loop, other than that, looks good

[sibirrer]

just checking whether this should be a jax for loop

[ahuang314]

python for loops are fine in situations where the number of iterations is less than 10