feat: Rpc bg switch

[koubaa]

Refactor python backend for rpc.

Add a hidden option to control which of the two threads is the main thread: rpc server, mechanical app. Change the default to mechanical app (in case the stability issue has to do with the background app)

[klmcadams]

I changed some variable names to use snake_case instead of camelCase and used pathlib instead of os (if possible). Also, I'd recommend changing functions & variables named f to something more descriptive (for example, service._exit_f, stop_f, start_f)

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.10% (target: -1.00%)	✅ 55.56%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (71aeaf2)	2507	2182	87.04%
Head commit (5cb8df5)	2510 (+3)	2187 (+5)	87.13% (+0.10%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1122)	9	5	55.56%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.

Project coverage is 87.13%. Comparing base (71aeaf2) to head (5cb8df5).
Report is 1 commits behind head on main.

❌ Your patch status has failed because the patch coverage (55.55%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1122      +/-   ##
==========================================
+ Coverage   87.03%   87.13%   +0.09%     
==========================================
  Files          39       39              
  Lines        2507     2510       +3     
==========================================
+ Hits         2182     2187       +5     
+ Misses        325      323       -2     

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