Add numerical support of other real types (laplace)

[huiyuxie]

Continue #1909.

Tasks:

• check laplace_diffusion 1d, 2d, 3d
• unit tests for above

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.30%. Comparing base (ba82d36) to head (b7493db).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2025      +/-   ##
==========================================
+ Coverage   95.35%   96.30%   +0.95%     
==========================================
  Files         466      466              
  Lines       37226    37227       +1     
==========================================
+ Hits        35495    35850     +355     
+ Misses       1731     1377     -354     

Flag	Coverage Δ
unittests	96.30% <ø> (+0.95%)	⬆️

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[huiyuxie]

BC tests are not easy to be implemented so I collected all of them #1987 to be done later.

Basically all the tests for src/equations are done except for some broken tests (mainly due to the functions from math.jl like ln_mean and inv_ln_mean) and maybe this is my next task.

Ready for review @ranocha

[ranocha]

Thanks! I have some minor suggestions.

[huiyuxie]

Sorry I forgot this issue please review again @ranocha ^^

[ranocha]

Thanks