Add FV particle diffusion operator

[jbreue16]

todo

• copy FV particle discretization from GRM_FV to new ParticleDiffusionOperatorFV and adapt to ParticleDiffusionOperatorBase interface
• enable ParticleDiffusionOperatorFV in GeneralRateParticle
• flip particle state
• move out jacobian from residual, similar to DG operator
• tests
  • add a generalized discretization setter to allow mixed discretizations in tests
  • reference tests
    • num.ref: LRMP DG == GRM bulk DG par FV with nparcell = 1 and sensitivities
    • linear binding analytical reference
    • GRM SMA LWE numref comparison with pure DG solution
    • another sensitivity test?
  • Jacobian
    • single component no bnd
    • 1 comp linear: with surfDiff, req binding
    • 2 comp linear: with surfDiff, kin binding
• Warning for nParCell = 1, wrong use of model
• documentation
• Add mixed bulk DG particle FV benchmark CADET-Verification#120

[codecov]

Codecov Report

❌ Patch coverage is 61.70732% with 157 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...bcadet/model/parts/ParticleDiffusionOperatorFV.cpp	60.80%	132 Missing and 24 partials ⚠️
...rc/libcadet/model/particle/GeneralRateParticle.cpp	80.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
...bcadet/model/parts/ParticleDiffusionOperatorDG.cpp	64.42% <100.00%> (ø)
...bcadet/model/parts/ParticleDiffusionOperatorDG.hpp	66.67% <ø> (ø)
...bcadet/model/parts/ParticleDiffusionOperatorFV.hpp	100.00% <100.00%> (ø)
...rc/libcadet/model/particle/GeneralRateParticle.cpp	70.19% <80.00%> (+1.86%)	⬆️
...bcadet/model/parts/ParticleDiffusionOperatorFV.cpp	60.80% <60.80%> (ø)

... and 3 files with indirect coverage changes