[GSoC] Introduction and Microproject: modernize t7412 submodule

Hi everyone,

My name is Yuvraj Singh Chauhan, and I am interested in contributing to Git for GSoC 2026. I have prior contributing experience with linux kernel and now I wish to work on GIT as well since these are the two projects I personally use a lot.

As part of my microproject, I would like to update the `test -f`, `test -d`, and `test -e` assertions to use `test_path_is_file`, `test_path_is_dir`, and `test_path_exists` helpers in the t7412 submodule.

Is this a suitable microproject for me to start working on?

Thanks, Yuvraj