Make value_and_pullback the primitive

[gdalle]

Core

• Make split reverse mode (value_and_pullback_split) depend on combined reverse mode (value_and_pullback), not the other way around
• Add pushforward!! and pullback!! for mutating functions (not sure about including y in the signature)
• Define pushforward extras for pullback in forward mode and vice versa

Docs

• Only guarantee numbers and arrays

Tests

• Add necessary tests and benchmark for new methods

Extensions

• Fix the reverse mode backends

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.94%. Comparing base (95fe3bd) to head (bf2d286).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
+ Coverage   93.65%   93.94%   +0.28%     
==========================================
  Files          61       61              
  Lines        2050     2098      +48     
==========================================
+ Hits         1920     1971      +51     
+ Misses        130      127       -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.