Support optionally running Python compiler services in-process

[ChrisCummins]

🚀 Feature

Motivation

The goal is to make it easier for developers to debug new compiler services by removing the inter-process comms layer that can obfuscate stack traces and make it harder to trace the cause of bugs. See #318.

Pitch

Extend the CompilerGym class constructor's service argument to take CompilationSession subclass type. This would then start an in-process gRPC server, enabling more debuggable tracebacks in case of failures:

>>> env = CompilerEnv(service=MyCompilationSession, rewards=..., dataset=...)

>>> env.step(action_that_fails)
Traceback: ...

Alternatives

Figure out a way to better propagate errors from compiler services that can be applied to all languages, not just Python.

Additional context

Thanks @hughleat for the suggestion and initial discussion.