[abhinav-phi]

Description

• m.proj: close the input and output files after the conversion.
• g.extension: close the /dev/null output handle in install_extension_win() and install_extension_std_platforms(); use a context manager for the probe read in fix_newlines().
• grass.pygrass.modules.interface.env.G_debug(): close GRASS_DEBUG_FILE after each message instead of leaking one handle per call.
• r.in.gdal testsuite: close the file read in test_r_in_gdal.py.

Motivation and context

Part of #8122. These are the remaining small, independent leaks listed there.

How has this been tested?

• G_debug(), called three times with GRASS_DEBUG_FILE set and PYTHONDEVMODE=1: before the change one ResourceWarning: unclosed file ... dbg.txt; after the change none.
• m.proj: the change closes handles after p.wait(); I could not run the reproducer here because GRASS 7.8 does not accept g.proj format=proj4, which current m.proj uses.
• g.extension: not run (needs an add-on download); the change only closes handles at the end of the two install functions and wraps one open() in with.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• PR title starts with a pre-defined prefix
• My code follows the code style of this project
• My change requires a change to the documentation
• I have added tests to cover my changes (covered by the reproducers in [Bug] Unclosed files and pipes in tool scripts and Python modules #8122)

AI assistance was used to prepare this change and the test results above.

[echoix]

Again, understand your changes, and do actual useful validations of your work. Grass 7.8 and anything other than the state of your branch is not useful