tests: add live integration test for get_region in grass.jupyter

[AkshadSonawane]

Hi! Following up on the feedback from #7180, I've completely rewritten these tests to drop the mocks and use a live GRASS session instead.

The new tests borrow the run_in_subprocess pattern from test_init_finish to spin up a live temporary project in isolation. They check that get_region() returns the expected geographic keys (n, s, e, w, nsres, ewres), and use abs() < 1e-6 for the float comparisons when verifying the dict reflects a g.region change. Tests are marked @pytest.mark.integration so they won't run unless explicitly called with pytest -m integration.
Verified the Python logic locally - full integration needs a compiled GRASS environment so leaning on CI for the live-session check, same as the existing test_init_finish tests do.

[petrasovaa]

GRASS pytests assume PYTHONPATH is already set up, just look how most pytests in GRASS look like. Also, please test locally, don't rely on CI.

[AkshadSonawane]

GRASS pytests assume PYTHONPATH is already set up, just look how most pytests in GRASS look like. Also, please test locally, don't rely on CI.

Thanks for the feedback, @petrasovaa! I've dropped the subprocess approach, switched to using the native session fixture from conftest.py, and verified everything locally this time. Updated tests are over at #7209.