working delta-sph and fix usage of "h_factor"

[JonasErbesdobler]

-implementation of delta-SPH for the current main branch
-kernel.h_factor can now be utilized

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 45.33333% with 41 lines in your changes missing coverage. Please review.

Project coverage is 65.5%. Comparing base (aa0e93a) to head (2d3b4cd).

Files	Patch %	Lines
jax_sph/solver.py	43.6%	40 Missing ⚠️
jax_sph/case_setup.py	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #19     +/-   ##
=======================================
- Coverage   66.4%   65.5%   -0.9%     
=======================================
  Files         11      11             
  Lines       1353    1418     +65     
=======================================
+ Hits         899     930     +31     
- Misses       454     488     +34     

Flag	Coverage Δ
unittests	65.5% <45.3%> (-0.9%)	⬇️

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