Sediment model fixes + simpler model

[jagoosw]

I've finally fixed sediment models so they work properly and conserve nitrogen!

Also fixed a few bugs in the sediment model time-stepping and adds a simple instant remineralization model (as described in PISCESv2 paper).

Hopefully after #120 is merged the odd commit history will be fixed.

[codecov]

Codecov Report

Patch coverage: 74.66% and project coverage change: +1.94 🎉

Comparison is base (d53ea6b) 61.90% compared to head (891fc26) 63.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #121      +/-   ##
==========================================
+ Coverage   61.90%   63.85%   +1.94%     
==========================================
  Files          27       28       +1     
  Lines         974     1021      +47     
==========================================
+ Hits          603      652      +49     
+ Misses        371      369       -2     

Impacted Files	Coverage Δ
src/Boundaries/Sediments/coupled_timesteppers.jl	68.00% <0.00%> (-12.96%)	⬇️
src/Models/AdvectedPopulations/LOBSTER/LOBSTER.jl	84.21% <60.00%> (+2.39%)	⬆️
src/Boundaries/Sediments/Sediments.jl	58.82% <62.50%> (-5.47%)	⬇️
src/Models/AdvectedPopulations/NPZD.jl	92.00% <66.66%> (+1.72%)	⬆️
...c/Boundaries/Sediments/instant_remineralization.jl	83.33% <83.33%> (ø)
src/Boundaries/Sediments/simple_multi_G.jl	89.79% <92.85%> (-2.31%)	⬇️
src/Models/Individuals/SLatissima.jl	83.87% <100.00%> (ø)
src/Models/Models.jl	100.00% <100.00%> (+100.00%)	⬆️
src/Particles/Particles.jl	29.41% <100.00%> (+1.63%)	⬆️

... and 2 files with indirect coverage changes

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[jagoosw]

Perhaps I should make sediments work with bathymetry here too

I think I will make another PR after this to change flat sediments to actually have flat fields, and to make them work with bathymetry which shouldn't be too hard and just means everytime we index into the k=1 cell of a field we go to the max depth index