Add influence classification for ConnectivityTracer

[gdalle]

• Revamp ConnectivityTracer to follow the blueprint of GradientTracer, except that it uses is_influence instead of is_firstder
• Add a new category of operators whose influence is zero, and distinguish them from those who have an influence but zero derivatives
• Handle big, widen, zero, one, oneunit, typemin, typemax, eps, float, floatmin, floatmax, maxintfloat like normal 1_to_1 operators when they are applied to numbers (not when they are applied to types)
• Add special case for when ForwardDiff cannot compute derivatives (we assume those derivatives are zero)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.77049% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 79.19%. Comparing base (efefcc7) to head (b3b2335).

Files	Patch %	Lines
src/operators.jl	57.69%	11 Missing ⚠️
src/overload_connectivity.jl	85.71%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #78      +/-   ##
==========================================
+ Coverage   77.30%   79.19%   +1.88%     
==========================================
  Files          14       14              
  Lines         617      644      +27     
==========================================
+ Hits          477      510      +33     
+ Misses        140      134       -6     

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[adrhill]

Thanks! :)