Remove directories leftover from improper shutdown so sage-cleaner won't kill random processes

[tornaria]

📚 Description

From #27769:

Under rare conditions, sage is killed at startup by sage-cleaner.

This requires:

Files left over in ~/.sage/temp/HOSTNAME/PID
A pid in ~/.sage/temp/HOSTNAME/PID/spawned_processes must exist, and be started at init time. Its process group id will be 0

When sage-cleaner tries to clean up, it will do a "kill 0", which will kill sage.

Files will only be left in ~/.sage/temp/HOSTNAME if sage is not shutdown properly. Most likely because of a reboot.

Even if the situation doesn't result on a "kill 0", sage-cleaner would still go on a killing spree for random processes which is awful.

The current PR removes everything under ~/.sage/temp/HOSTNAME/ at sage-cleaner startup so this doesn't happen.

Since sage-cleaner won't run more than once at a time, this seems safe.

Fixes #27769

📝 Checklist

• I have made sure that the title is self-explanatory and the description concisely explains the PR.
• I have linked an issue or discussion.

[tornaria]

I was hit by this bug and I wasn't able to even start sage. I found the ticket with a ready to review patch. I cherry-picked the commit into my current sage and voila: everything worked.

I looked at the code and comments, and I think it's a good solution so I'm giving it a positive review.

Component: scripts

Keywords: sage-cleaner

Author: Andy Howell

[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: 2b155c7

[codecov-commenter]

Codecov Report

Base: 88.60% // Head: 88.59% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (2b155c7) compared to base (8f5bbd2).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35204      +/-   ##
===========================================
- Coverage    88.60%   88.59%   -0.01%     
===========================================
  Files         2140     2140              
  Lines       397273   397273              
===========================================
- Hits        352004   351966      -38     
- Misses       45269    45307      +38     

Impacted Files	Coverage Δ
src/sage/interfaces/qsieve.py	71.30% <0.00%> (-2.61%)	⬇️
src/sage/graphs/generators/random.py	91.43% <0.00%> (-1.20%)	⬇️
src/sage/schemes/elliptic_curves/hom_velusqrt.py	94.09% <0.00%> (-1.19%)	⬇️
src/sage/coding/channel.py	97.10% <0.00%> (-0.73%)	⬇️
src/sage/modular/modform/numerical.py	94.19% <0.00%> (-0.65%)	⬇️
...sage/geometry/hyperbolic_space/hyperbolic_model.py	88.95% <0.00%> (-0.62%)	⬇️
src/sage/modular/arithgroup/congroup_gamma0.py	94.41% <0.00%> (-0.56%)	⬇️
src/sage/sets/integer_range.py	91.41% <0.00%> (-0.51%)	⬇️
src/sage/graphs/tutte_polynomial.py	93.57% <0.00%> (-0.46%)	⬇️
src/sage/graphs/generic_graph.py	89.12% <0.00%> (-0.46%)	⬇️
... and 19 more

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