Minor hessian fix

[gdalle]

DI source

• Fuse the map and reduce(hcat/vcat) for Jacobian and Hessian. This makes jacobian and hessian type-unstable, see the MWE on Discourse. Not doing this change for now.
• Get rid of two useless lines in hessian.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.48%. Comparing base (f663225) to head (21a28f6).

❗ There is a different number of reports uploaded between BASE (f663225) and HEAD (21a28f6). Click for more details.

HEAD has 55 uploads less than BASE

Flag	BASE (f663225)	HEAD (21a28f6)
DI	66	24
DIT	16	3

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #561       +/-   ##
===========================================
- Coverage   98.39%   78.48%   -19.92%     
===========================================
  Files         107      105        -2     
  Lines        4739     4703       -36     
===========================================
- Hits         4663     3691      -972     
- Misses         76     1012      +936     

Flag	Coverage Δ
DI	87.59% <100.00%> (-11.05%)	⬇️
DIT	59.25% <ø> (-38.65%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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