graphIO: serialize username that saved the file

[Alxiice]

Description

In the serialized file, save the username that last saved the file.
It could be interesting for stat purposes, we can get the modification date with statbut not the username easily.

[gemini-code-assist]

Code Review

This pull request adds the current username to the serialized file header using getpass.getuser(). Feedback suggests wrapping the getpass.getuser() call in a try-except block to prevent potential crashes in environments where user information is unavailable, such as containerized or headless systems.

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.32%. Comparing base (364ccbb) to head (a2741e2).
⚠️ Report is 9 commits behind head on develop.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/graphIO.py	66.66%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (66.66%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3134      +/-   ##
===========================================
- Coverage    85.33%   85.32%   -0.01%     
===========================================
  Files           73       73              
  Lines        11414    11420       +6     
===========================================
+ Hits          9740     9744       +4     
- Misses        1674     1676       +2     

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