Make `Runtime::run` Return Lua Values

[CompeyDev]

This PR intends to return a more meaningful output for Runtime::run invocations. Instead of only returning an ExitCode, Runtime::run now returns a tuple including a Vec of values returned by the lua thread.

TODO:

• [x] Return the actual exit code instead of an enum variant
  • [x] Depends on https://github.com/lune-org/mlua-luau-scheduler/pull/1 to be merged
• [x] Return lua values
  • [x] Update dependents to consume tuple

Once merged, this closes #175 and closes #92.