Investigate splitting factor operational part from 'constant' part of factor

[Affie]

If it can be split so that factor solver data only contains the working memory serialization becomes easy as solver data is just ignored and rehydrated when unpacked for use by the solver and there can possibly be no PackedFactor.

• What fields are always constant?
  • DF: Almost everything in FactorNodeData is constant and can move to FactorFDG -- but, need to checking how CCW is built upon FactorCompute
• Include CI test for more complicated factor type such as (i.e. not in Distributions.jl):
  • IMU: https://github.com/JuliaRobotics/RoME.jl/blob/ca98e9c18f8837d92863cb798eb7f1ec5adcbbfc/src/factors/Inertial/IMUDeltaFactor.jl#L540-L568
  • LIDAR: https://github.com/NavAbility/NavAbilitySDK.jl/blob/4bddd83fd1d66cf88077f9a69871df3b4530621d/test/unit/testFactors.jl#L61-L68
    • Notes: serialization for that ScatterAlign factor uses preambleCache and works for either parched or unparched serialization modes. https://github.com/JuliaRobotics/Caesar.jl/blob/develop/test/testStashing_SAP.jl
  • APRILTAGS: https://github.com/JuliaRobotics/Caesar.jl/blob/develop/test/testPose2AprilTag4Corner.jl
  • SASBearing2D: https://github.com/JuliaRobotics/Caesar.jl/blob/9df2df54d4a1bc271afafd5730d35c95af4c67f5/src/beamforming/SASBearing2D.jl#L219-L313
  • FLUX.jl NNFactors: https://github.com/JuliaRobotics/IncrementalInference.jl/blob/dab3ca94bfb937629aa3e2751d3c5bf2f84d75fe/test/testFluxModelsDistribution.jl#L66-L68
  • DEFactors (no serialization yet): https://github.com/JuliaRobotics/IncrementalInference.jl/blob/develop/test/testDERelative.jl
• Can we build factor data (w.r.t. the compute part FactorOperationalMemory/CCW) lazily from DFG and only "inflate" when used in IIF. That is, move reconstFactorData out of DFG.
• TODO...

'constant' in this case means not changed by the solver

In other words:
Should we move non FactorOperationalMemory to DFGFactor:
Maybe: fnc, multihypo, nullhypo, inflation ?
that way we split solverData <: FactorOperationalMemory and constants

[Affie]

Note on CCW: currently, only hyporecipe.certainhypo and usrfnc! are pulled out of CCW to be persisted, the rest are thrown away.
Also code TODO: improve _createCCW for hypotheses and certainhypo field recovery when deserializing reconstitute from stored data