[Linux] fix Process.open_files() for cases fdinfo has only flags (#2596)

[orionlee]

Summary

• OS: Linux
• Bug fix: yes
• Type: core
• Fixes: Process.open_files() raises IndexError in some linux environments #2596

Description

Fix the issue in Process.open_files() in Google Cloud Run + Docker Linux Python image environment, where the fdinfo file of an opened file does not have the pos: line expected by existing psutil codes.

History and Credit additions

For HISTORY.rst:

- 2596_, [Linux]: `Process.open_files()` raises some IndexError in some environments
  such as Docker + Google Cloud Run

For CREDITS:

N: Sam Lee
W: https://github.com/orionlee
I: 2596

[christopher5106]

please merge

[christopher5106]

                    ntuple = popenfile(
                        path, int(fd), int(pos), mode, flags
                    )
                    retlist.append(ntuple)

does not work when pos is None

[orionlee]

• Updated so that pos, flag would be 0s if they are not defined in the underlying fdinfo file
• The failing test in CI ( macos-15, arm64 ) appears to be some unrelated issues on master.