Create very simple RPC so the subprocess loads functions

[callumforrester]

Fixes #590

[codecov]

Codecov Report

Attention: Patch coverage is 95.34884% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.84%. Comparing base (5351741) to head (b5f537d).

Files	Patch %	Lines
src/blueapi/service/runner.py	94.11%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #584      +/-   ##
==========================================
- Coverage   92.86%   92.84%   -0.02%     
==========================================
  Files          40       40              
  Lines        1793     1818      +25     
==========================================
+ Hits         1665     1688      +23     
- Misses        128      130       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[DiamondJoseph]

Approving for the _rpc function, if @callumforrester can approve for the other changes I made ;)

[joeshannon]

Is there an associated issue for this? I can't quite infer what the problem was from this PR. Presumably pickle related?

[DiamondJoseph]

I can't quite infer what the problem was from this PR. Presumably pickle related?

I assume so from Callum's first commit (but surely still has to pickle the args, kwargs just not the function?), my interest in it is it makes upcoming observability handling easier

[callumforrester]

I've made a retroactive issue: #590