Control point Enzyme gradients with CUDABackend

[SouthEndMusic]

The custom reverse rule seems to have made the code stable, but (pre)compile time is extremely long

To do:

• Add FiniteDiff.jl comparison test for the loss function

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 20.00000% with 16 lines in your changes missing coverage. Please review.

Project coverage is 91.71%. Comparing base (802171d) to head (ed2f496).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
ext/SplineGridsEnzymeExt.jl	18.75%	13 Missing ⚠️
src/spline_grid.jl	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #96      +/-   ##
==========================================
- Coverage   92.94%   91.71%   -1.24%     
==========================================
  Files          15       15              
  Lines        1191     1207      +16     
==========================================
  Hits         1107     1107              
- Misses         84      100      +16     

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