Consolidate Stats Handling

[avik-pal]

Fixes #410

Oops lost my local changes it seems...

Merge after #435

[avik-pal]

Now cache.stats gives the total counts correctly. For polyalgorithms this means we get the accumulated stats from all the solve calls.

[avik-pal]

cc @oscardssmith because you needed this in OrdinaryDiffEq.

[codecov]

Codecov Report

Attention: Patch coverage is 94.28571% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 86.42%. Comparing base (86bb307) to head (50aa5c4).
Report is 2 commits behind head on master.

Files	Patch %	Lines
src/default.jl	75.00%	1 Missing ⚠️
src/descent/steepest.jl	0.00%	1 Missing ⚠️
src/internal/jacobian.jl	87.50%	1 Missing ⚠️
src/internal/operators.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #437      +/-   ##
==========================================
- Coverage   86.46%   86.42%   -0.05%     
==========================================
  Files          47       47              
  Lines        2904     2865      -39     
==========================================
- Hits         2511     2476      -35     
+ Misses        393      389       -4     

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[oscardssmith]

This change appears to have broken SciML/OrdinaryDiffEq.jl#2167. Do you want to make the corresponding OrdinaryDiffEq change or should I?

[avik-pal]

Can you do it? I am not sure what broke, this was a purely internal API change

[oscardssmith]

will do. The problem was that OrdinaryDiffEq with NonlinearSolveAlg runs the step!(cache) loops of a nonlinear solver itself and was using nf to determine how many calls the step! had made to update the integrator's stats.