Simplify batched mode `pushforward`, `pullback` and `hvp`

[gdalle]

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 99.62406% with 3 lines in your changes missing coverage. Please review.

Project coverage is 93.63%. Comparing base (56fc186) to head (281e852).

Files with missing lines	Patch %	Lines
...rentiationInterface/src/first_order/pushforward.jl	92.68%	3 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #412      +/-   ##
==========================================
- Coverage   97.33%   93.63%   -3.71%     
==========================================
  Files         104      102       -2     
  Lines        4922     4885      -37     
==========================================
- Hits         4791     4574     -217     
- Misses        131      311     +180     

Flag	Coverage Δ
DI	99.27% <99.58%> (-0.08%)	:arrow_down:
DIT	86.33% <100.00%> (-8.47%)	:arrow_down:

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