Add RunContext support for script outputs (#765)

Resolves #667

This PR:

- Introduces a new field in the project file: `scriptType` which has the
default value of `Class` (in parity with previous versions), but can
also be `RunContext`.
- This is then passed to `InstanceContext` from the `Project` struct.
- This then changes the RunContext in the lua `snapshot_middleware`

---------

Co-authored-by: Micah <dekkonot@rocketmail.com>

tests/tests/build.rs

@@ -44,6 +44,7 @@ gen_build_tests! {
     json_model_legacy_name,
     module_in_folder,
     module_init,
+    nested_runcontext,
     optional,
     project_composed_default,
     project_composed_file,