Separate testing scenarios for each operator

[adrhill]

Opening this as a draft PR for feedback before updating the default scenarios in src/scenarios.

[gdalle]

Testing

• Create scenario types specific to each operator
• Document most of it in the docstring of AbstractScenario
• Add minimal type constraints in the scenario type parameters
• Write the correct constructors
• Apply them to the default, GPU, static and component test suites
• Update the correctness, type stability, call count, sparsity and benchmark subroutines
• Pass the ref_backend from above if needed to override scenario-specific reference
• Replace @info with ProgressMeter.jl to avoid flushing the terminal

Docs

• Create TOC sections on the sidebar
• Separate core and testing API references
• Separate extensions from backends

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.31461% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 94.54%. Comparing base (78d3d99) to head (88128c1).

Files	Patch %	Lines
...entiationInterfaceTest/src/test_differentiation.jl	91.17%	3 Missing ⚠️
...DifferentiationInterfaceTest/src/tests/sparsity.jl	80.00%	2 Missing ⚠️
...fferentiationInterfaceTest/src/tests/call_count.jl	96.87%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #120      +/-   ##
==========================================
+ Coverage   93.76%   94.54%   +0.78%     
==========================================
  Files          59       59              
  Lines        1828     1798      -30     
==========================================
- Hits         1714     1700      -14     
+ Misses        114       98      -16     

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