chore: debug Enzyme tests

[gdalle]

Claude seems to think that fixing these two Enzyme bugs would resolve the red CI:

• MethodError: no method matching blocks(::LLVM.ConstantExpr) EnzymeAD/Enzyme.jl#2925
• Latest Enzyme version broke DI tests with new runtime activity error EnzymeAD/Enzyme.jl#2854

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 3.30%. Comparing base (5572e56) to head (71fb5d9).

❗ There is a different number of reports uploaded between BASE (5572e56) and HEAD (71fb5d9). Click for more details.

HEAD has 68 uploads less than BASE

Flag	BASE (5572e56)	HEAD (71fb5d9)
DI	58	2
DIT	12	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #1023       +/-   ##
==========================================
- Coverage   98.21%   3.30%   -94.92%     
==========================================
  Files         138     101       -37     
  Lines        8131    5633     -2498     
==========================================
- Hits         7986     186     -7800     
- Misses        145    5447     +5302     

Flag	Coverage Δ
DI	3.30% <100.00%> (-95.67%)	⬇️
DIT	?

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[gdalle]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved the merge conflict in .github/workflows/Test.yml. The conflict arose because main added test-DI-Core and test-DIT jobs while this branch had intentionally removed them to focus on Enzyme debugging. The merge keeps only the test-DI-Backend (Enzyme) job, consistent with the PR's purpose, while pulling in all other changes from main.