Make Enzyme the only compatible AD engine

[ptiede]

Ok so from testing, Enzyme looks ready to go for almost everything! Almost all of the examples are switched over to Enzyme and some of the testing still needs to be patched.

Before merging the following issues/PR's will need to be solved

• Sparse matvec seems strangely slow compared to Zygote EnzymeAD/Enzyme.jl#1682
• Missing rules for FFTW unsafe_execute EnzymeAD/Enzyme.jl#1717
• Make system solely compatible with Enzyme EHTJulia/VLBISkyModels.jl#54
• Enzyme is dropping gradients when using custom rule and views EnzymeAD/Enzyme.jl#1856
• Gradients are dropped when using a sparse cholesky EnzymeAD/Enzyme.jl#1825

Now for the exciting part I am seeing pretty large performance boosts both for the forward and reverse passes. The forward pass is faster because Enzyme makes me able to do a lot more in place and revert some coding styles that were needed to get Zygote to be somewhat efficient.

For the reverse pass before this PR I would typically see reverse pass speeds that were 4-6x slower than the forward pass. After this PR it is typically between 2-4x. The biggest gains are really for polarized modeling.

This will be a breaking change however so this will push a new Comrade version (sorry people)

[codecov]

Codecov Report

Attention: Patch coverage is 54.43787% with 77 lines in your changes missing coverage. Please review.

Project coverage is 89.19%. Comparing base (b9fd00e) to head (eff6418).
Report is 55 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rules.jl	0.00%	47 Missing ⚠️
src/instrument/model.jl	72.72%	9 Missing ⚠️
src/instrument/priors/array_priors.jl	36.36%	7 Missing ⚠️
src/instrument/site_array.jl	37.50%	5 Missing ⚠️
src/posterior/vlbiposterior.jl	16.66%	5 Missing ⚠️
src/mrf_image.jl	92.00%	2 Missing ⚠️
src/instrument/jonesmatrices.jl	94.73%	1 Missing ⚠️
src/posterior/abstract.jl	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #364      +/-   ##
==========================================
- Coverage   92.50%   89.19%   -3.31%     
==========================================
  Files          30       30              
  Lines        1574     1583       +9     
==========================================
- Hits         1456     1412      -44     
- Misses        118      171      +53     

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[ptiede]

I am going to merge this now. All the Enzyme issues either have rules now to get around them or utilize a ChainRulesRule