Detects a test file based on attribute tags

[waynebowie99]

This is to fix #33

is_test_file was returning true for all files that were part of the test project

[Nsidorenco]

Hey 👋🏻
This is a pretty good idea! Unfortunately doing it in this way makes the adapter less general since you would be breaking any test adapter that is not XUnit or NUnit regex matching the files like this.

The only way to do this (as I see it) would be to use the vstest/mtp client to see if the file actually contains any tests, but at this point of the neotest pipeline I'm not sure we want to block waiting for the test client.

Another point I'm not quite sure of, is how neotest deals with files that have been marked as a "non-test file". What happens if the file is updated to contain tests, will neotest continue to ignore the file or will it trigger a rescan?