Add ToJSON/FromJSON instances for EraScript
* Add ToJSON/FromJSON as superclass constraints to EraScript * Add ToJSON/FromJSON instances for MultiSig, Timelock and DijkstraNativeScript * Add structured JSON serialisation for native scripts across all eras (Shelley, Allegra, Dijkstra) * Add ToJSON/FromJSON instances for AlonzoScript with structured JSON format * Rename kindObject (returning Value) to kindObjectValue; add new kindObject returning Aeson.Object * Fix shelleyBasedEraNativeScriptToJSON and sizedNativeScriptGens to accept a child continuation to correctly handle nested scripts across eras * Add round-trip JSON property tests for NativeScript and Script to the shared era spec
