Fix size-1 Jacobian with Enzyme

[gdalle]

DI extensions

• Use onehot instead of chunkedonehot to initialize shadows for Enzyme's Jacobian when the batch size is 1

DIT source

• Add functions from $R^1$ to $R^1$ to the default scenarios

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.58%. Comparing base (5419f9a) to head (400f365).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #374   +/-   ##
=======================================
  Coverage   96.57%   96.58%           
=======================================
  Files          99       99           
  Lines        4876     4887   +11     
=======================================
+ Hits         4709     4720   +11     
  Misses        167      167           

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