Fix POSIX ioctls on big-endian systems (s390x for example)

[EdwardBetts]

I've made a Debian package for serialx, the package is available here: https://tracker.debian.org/pkg/python-serialx

Debian runs on lots of architectures including s390x. The s390x architecture is interesting because it is big-endian, there aren't many big-endian architectures left. The Debian CI infrastructure identified endian related bugs when running the tests on s390x.

I've modified the code to fix these bugs and serialx now runs happily on the s390x architecture.

Just to warn you I did get assistance from a coding agent when writing this fix. I don't know if you have a policy about AI contributions, but I thought it was important to let you know.

[puddly]

Thanks! I haven't run into endianness issues in a long while 😄.

Just to warn you I did get assistance from a coding agent when writing this fix. I don't know if you have a policy about AI contributions, but I thought it was important to let you know.

As long as you've tested it (or it passes some form of CI) there's no issues at all. This is a pretty small PR.

[puddly]

Looks like little endian CI passes so this should be good to go.

My apologies for the linter failure, I forgot to update our README to include this step:

uv pip install '.[dev]'
prek run --all-files

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.35%. Comparing base (4a1818c) to head (9274335).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #104      +/-   ##
==========================================
+ Coverage   92.15%   92.35%   +0.19%     
==========================================
  Files          22       22              
  Lines        3660     3661       +1     
==========================================
+ Hits         3373     3381       +8     
+ Misses        287      280       -7     

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