Fixes: #2288

This PR does:

• Add flag to kprovex called --emit-json-spec which emits the spec module as JSON to the specified file.
• Fixes the JSON serialization of KImport to include the node header (all KAST JSON terms must have node header).
• Adds unit tests of the pyk library which do:
  • Serialize pretty proof to json using new flag -> read json proof in pyk and write out as pretty to file -> run kprovex on the newly serialized proof using pyks KProve.prove()
  • Serialize pretty proof to json using new flag -> read json proof in pyk and prove using KProve.proveClaim().