feat: allow and test holomorphic derivatives

[gdalle]

Complex number compatibility (first order only):

• Make sure that pullback returns the product with the adjoint (conjugate transpose) of the Jacobian
• Add conjugation in reverse-mode Jacobians, dense and sparse
• Document that we assume functions to be holomorphic when dealing with complex inputs

Complex number testing:

• Create test scenarios with complex holomorphic functions, first order only
• Test these scenarios with FiniteDiff (ForwardDiff doesn't work)

[codecov]

Codecov Report

Attention: Patch coverage is 96.72131% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.61%. Comparing base (4feb596) to head (af0aa37).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...fferentiationInterface/src/first_order/jacobian.jl	83.33%	1 Missing ⚠️
...ifferentiationInterface/src/misc/from_primitive.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #687      +/-   ##
==========================================
- Coverage   97.61%   97.61%   -0.01%     
==========================================
  Files         114      115       +1     
  Lines        5623     5650      +27     
==========================================
+ Hits         5489     5515      +26     
- Misses        134      135       +1     

Flag	Coverage Δ
DI	98.74% <93.54%> (-0.03%)	⬇️
DIT	95.39% <100.00%> (+0.04%)	⬆️

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