fix: Preserve interruptible syscalls when registering the SIGINT handler

[skmendez]

Resolves #21739. Before registering the SIGINT handler, we check the current state of SA_RESTART, and if it's not already set, we disable it after running signal_hook::low_level::register. The maintainer of signal-hook does not want to support this feature (see discourse at vorner/signal-hook#153), so options for resolving this are either to reimplement cross-platform signal handling here or to just do this sigaction workaround.

Copying the minimal example from #21739 (comment):

import polars

# you can now ctrl+c this!
input()

Note that originally I tried to add unit tests for this fix, but getting a unit test of signal handling behavior working consistently on high-contention CI machines proved fairly difficult, and the original KeyboardInterrupt logic is already also untested AFAICT, so I dropped these tests. Happy to try to readd them if there's interest though.

AI usage disclosure:
I used codex to write the fix, based on the workaround discussed in vorner/signal-hook#153. This commit message and all code comments (including the SAFETY comments) were written by me. I have manually reviewed all changes and I believe they are correct.

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[codecov]

Codecov Report

❌ Patch coverage is 65.51724% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.50%. Comparing base (df59905) to head (afc4eda).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-error/src/abort.rs	65.51%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #28805      +/-   ##
==========================================
+ Coverage   81.27%   81.50%   +0.23%     
==========================================
  Files        1887     1887              
  Lines      266898   266916      +18     
  Branches     3238     3238              
==========================================
+ Hits       216908   217561     +653     
+ Misses      49163    48528     -635     
  Partials      827      827              

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