Cherry-pick #17188 to 7.x: Harden system/package parsing of deb size

[adriansr]

Cherry-pick of PR #17188 to 7.x branch. Original message:

What does this PR do?

Fixes system/package dataset parsing of Deb package's Installed-Size field in order to:

• Do not fail package enumeration when a malformed value is found.
• Understand prefixes k/K, m/M and G/b to report a size in line with what the maintainer meant.

Why is it important?

Deb packages report their installed size in a field, Installed-Size, which is an integer interpreted as KiB. Some rare third-party packages are adding a unit at the end of this field, by mistake:

Installed-Size: 65M

System tools dpkg/apt ignore everything after the number. However, Auditbeat is currently failing to parse the list of packages once this malformed field is reached.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• n/a I have made corresponding changes to the documentation
• n/a I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works

How to test this PR locally

To generate a package with a malformed Installed-Size:

dpkg-deb -R /var/cache/apt/archives/some-package.deb target_dir
vim target_dir/DEBIAN/control
dpkg-deb -b target_dir new-package.deb

Related issues

Fixes #16661

Logs

failed to get packages: error getting DEB packages: error converting 356K to int: strconv.ParseUint: parsing "356K": invalid syntax

failed to get packages: error getting DEB packages: error converting 25G to int: strconv.ParseUint: parsing "25G": invalid syntax