Conforming to pylint

[PiispaH]

No functional changes. Fixed the majority of warnings issued by pylint. Mainly the same warnings as mentioned in this PR are still around.

Checklist before merging

• Code has been formatted by black & isort
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 57.28155% with 44 lines in your changes missing coverage. Please review.

Project coverage is 62.77%. Comparing base (18782a8) to head (84a90ca).

Files	Patch %	Lines
...ne/execution_managers/conda_kernel_spec_manager.py	0.00%	8 Missing ⚠️
...execution_managers/persistent_execution_manager.py	50.00%	5 Missing ⚠️
spine_engine/server/remote_execution_service.py	0.00%	4 Missing and 1 partial ⚠️
spine_engine/utils/queue_logger.py	37.50%	5 Missing ⚠️
spine_engine/server/engine_server.py	55.55%	4 Missing ⚠️
...ine/execution_managers/kernel_execution_manager.py	70.00%	3 Missing ⚠️
spine_engine/project_item/executable_item_base.py	0.00%	2 Missing ⚠️
spine_engine/server/certificate_creator.py	0.00%	2 Missing ⚠️
spine_engine/utils/serialization.py	0.00%	2 Missing ⚠️
...ine/execution_managers/conda_kernel_spec_runner.py	0.00%	1 Missing ⚠️
... and 7 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
+ Coverage   62.69%   62.77%   +0.07%     
==========================================
  Files          40       40              
  Lines        3855     3844      -11     
  Branches      767      766       -1     
==========================================
- Hits         2417     2413       -4     
+ Misses       1290     1283       -7     
  Partials      148      148              

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