Batched HVP

[gdalle]

DI source

• Implement batched HVP from batched pushforward or pullback. Works for every mode except reverse-over-forward, where we need to be more subtle.
• Change some indexing in pushforward and pullback to have b in 1:B

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.58%. Comparing base (86f1e02) to head (d5014b8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #330      +/-   ##
==========================================
+ Coverage   96.56%   96.58%   +0.02%     
==========================================
  Files          96       96              
  Lines        4625     4660      +35     
==========================================
+ Hits         4466     4501      +35     
  Misses        159      159              

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