Fix partial writes for coredumps larger than 2 GiB

[bdrung]

Python's os.write() is a low-level POSIX call that directly maps to the write(2) system call. The write(2) man page says:

On Linux, write() (and similar system calls) will transfer at most 0x7ffff000 (2,147,479,552) bytes, returning the number of bytes actually transferred.

Because os.write() does not handle looping, writing raw bytes coredumps larger than 2 GiB results in truncated files of exactly 0x7ffff000 bytes, which are then reported as corrupted by gdb.

In data/apport loop over os.write until the whole coredump is written since that scripts operate on low level. In apport.report use os.fdopen to operate on a high-level file object to safely write all bytes.

Bug: https://launchpad.net/bugs/2109979

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.50%. Comparing base (7ce5916) to head (68dcd1b).

Files with missing lines	Patch %	Lines
data/apport	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #647      +/-   ##
==========================================
+ Coverage   84.48%   84.50%   +0.01%     
==========================================
  Files         106      106              
  Lines       21044    21047       +3     
  Branches     3192     3194       +2     
==========================================
+ Hits        17780    17786       +6     
+ Misses       2790     2788       -2     
+ Partials      474      473       -1     

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