[abhinav-phi]

Description

Close files and pipes that these vector tools open and never close:

• v.rast.stats: close the gs.pipe_command() stdout in get_nr_of_categories() and perform_stats(); remove the unused nuldev and its os import.
• v.db.droptable: use a context manager for the /dev/null handle.
• v.db.univar, v.db.reconnect.all: close the module-level /dev/null handle in a finally.
• v.report: close the four gs.pipe_command() stdouts and the /dev/null handle.
• v.in.e00: close the /dev/null handle after use.

Motivation and context

Part of #8122. With PYTHONDEVMODE=1 these tools report unclosed files and pipes.

How has this been tested?

The reproducers from #8122, run with PYTHONDEVMODE=1:

• v.rast.stats: before the change v.rast.stats.py:212: ResourceWarning: unclosed file <_io.BufferedReader name=5> plus a /dev/null warning; after the change neither, and the r_average column is still created.
• v.db.droptable: before v.db.droptable.py:125: ResourceWarning: unclosed file <_io.TextIOWrapper name='/dev/null' ...>; after the change no warning.

Tested against GRASS 7.8 from the system package because this machine cannot build main (needs GDAL 3.7+, has 3.4). The changed code paths are version independent.

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 existing 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]

Testing against grass 7.8 is not valid at all. It’s really really old and different than the state we are now, code quality-wise