refactor(developer): complete fs move out of kmcmplib

* Moves filesystem access out of kmcmplib into kmc-kmn
* Adds filesystem access callback to kmcmplib unit tests
* Cleans up callback interface through wasm
* Adds unit tests for various file load scenarios
* Removes nodefs dependency from kmcmplib wasm build, and removes
  corresponding path mappings which were previously required for wasm
  builds; note that these are still present for the unit tests for
  kmcmplib.