Allow choice of AD backend for conditions

[gdalle]

Fixes #69

At the moment this works with default/adaptive backend and with ForwardDiffBackend() but not with ZygoteBackend(). I suspect this might be a bug in AbstractDifferentiation.jl (maybe AD#63). @mohamed82008 could you take a look? I skipped the problematic tests in test/systematic.jl and marked them with TODO.

@thorek1 wanna take this branch out for a spin and see if it solves your problem?

This PR also changes the constructor syntax in a breaking way: f and c are positional arguments, along with HandleByproduct(), but linear_solver becomes a kwarg along with the new conditions_backend

[codecov]

Codecov Report

Patch coverage: 93.33% and project coverage change: -0.23% ⚠️

Comparison is base (5990573) 91.83% compared to head (450a63c) 91.60%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #80      +/-   ##
==========================================
- Coverage   91.83%   91.60%   -0.23%     
==========================================
  Files           9        9              
  Lines         147      143       -4     
==========================================
- Hits          135      131       -4     
  Misses         12       12              

Files Changed	Coverage Δ
src/ImplicitDifferentiation.jl	66.66% <ø> (ø)
src/conditions.jl	71.42% <66.66%> (ø)
ext/ImplicitDifferentiationChainRulesExt.jl	100.00% <100.00%> (ø)
ext/ImplicitDifferentiationForwardDiffExt.jl	100.00% <100.00%> (ø)
src/implicit_function.jl	84.21% <100.00%> (-3.79%)	⬇️

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[gdalle]

Closing because this is completely outdated due to #86