Dont nest JSON strings in pre JSON structs (FactorDFG)

[dehann]

Every node should contain only native JSON

• Investigate splitting factor operational part from 'constant' part of factor #992
• defFactorType macro #1077
• Dont nest JSON strings in pre JSON structs (FactorDFG) #1118
• drop scalar type override JSON = String NavAbility/NavAbilitySDK.rs#37

This should be just a JSON dict, not a JSON3.write ::String:

• DistributedFactorGraphs.jl/src/entities/DFGFactor.jl

  Line 161 in 5306532

  data = JSON3.write(factordata),

[dehann]

ping @Affie

[Affie]

related: #992 and #1077