Improve handling for unsupported core files

[godlygeek]

Explicitly reject core files with a different endianness than the host. These would never have worked, but until now the reason wasn't clearly surfaced to the user.

Prevent reading past the end of a truncated or malformed core file's NT_FILE note.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.95652% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.92%. Comparing base (7bf481e) to head (7c6594f).

Files with missing lines	Patch %	Lines
src/pystack/_pystack/corefile.cpp	76.92%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #358      +/-   ##
==========================================
- Coverage   77.94%   77.92%   -0.02%     
==========================================
  Files          58       58              
  Lines        6693     6719      +26     
  Branches      631      635       +4     
==========================================
+ Hits         5217     5236      +19     
- Misses       1476     1483       +7     

Flag	Coverage Δ
cpp	77.92% <86.95%> (-0.02%)	⬇️
python	77.92% <86.95%> (-0.02%)	⬇️

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