File staging

[hategan]

This PR adds file staging to some executors (local and the batch family).

• It does so mostly through templates.
• It addresses the status updates issues mentioned in Added file staging job-api-spec#164 using a UDP service that simple netcat commands (and we have to carefully test there because there might be multiple versions of that tool) can send from the batch script. As a backup (if not netcat can be found), a file is used.
• Solves the issue of the state order inversion vs. when-is-the-native-id-available in the local executor by making the local executor template based (like the batch scheduler ones) and implementing staging as it is done in the batch scheduler executors. This has the disadvantage that it only delays finding a better solution for the native_id/order issue that will inevitably happen with synthetic-staging executors, but the plus is that the local executor is closer, for testing purposes, to the batch scheduler ones.
• Adds some testing tools for managing temporary files/directories
• Ensures that polling threads for batch scheduler executors are shut down when the executor is GC-ed

[codecov]

Codecov Report

❌ Patch coverage is 88.80597% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.00%. Comparing base (0c14103) to head (01a0663).
⚠️ Report is 43 commits behind head on main.

Files with missing lines	Patch %	Lines
src/psij/staging.py	82.60%	20 Missing ⚠️
src/psij/utils.py	89.09%	18 Missing ⚠️
tests/_test_tools.py	76.00%	12 Missing ⚠️
tests/conftest.py	31.25%	11 Missing ⚠️
...c/psij/executors/batch/batch_scheduler_executor.py	84.90%	8 Missing ⚠️
src/psij/executors/local.py	86.66%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #450      +/-   ##
==========================================
+ Coverage   74.92%   75.00%   +0.07%     
==========================================
  Files          94       91       -3     
  Lines        3972     4568     +596     
==========================================
+ Hits         2976     3426     +450     
- Misses        996     1142     +146     

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