hotfix: resolve pytest db deadlock (extracted from Saurabhsing21 PR #707

[CODEAbhinav-art]

Tracking PR

• Name: Abhinav Mishra
• Affiliation/Title: GSV, Contributor

Purpose of the PR

Unblocks the global backend CI pipeline by resolving an "idle in transaction" database deadlock during pytest teardown.

Summary

The pytest --cov job is currently hanging indefinitely across all open PRs after successfully completing test_cell_search_by_name. This is caused by tests not properly cleaning up SQLAlchemy sessions, leaving Postgres locked.

@Saurabhsing21 already successfully diagnosed and wrote the fix for this in backend/tests/conftest.py as part of his larger CSV streaming PR (#707). Because the maintainers are currently bandwidth-limited with finals week, I have extracted only Saurabh's conftest.py test harness improvements into this standalone hotfix.

Merging this will turn the backend checks green for all other contributors, allowing Saurabh's #707 to pass CI as well. All credit for this code goes to Saurabh.

Development Environment

• OS: Linux (Ubuntu)
• Python/Docker version: Python 3.11

Task List

• Updated the CHANGELOG.md
• Static code analysis passes
• All environments can be built
• All tests pass
• Clear documentation for new code (N/A)
• Linting passes

Relevant Issues

Closes #708

[jmadden173]

I tested this locally and it was functional. Only error I got was an existing broken test case.

init_database = <FlaskClient <Flask 'api'>>

    def test_get_teros_obj_fraction_scales_to_percent(init_database):
        """
        GIVEN adjusted VWC stored as a fraction
        WHEN TEROS data is retrieved
        THEN VWC is returned as a percentage
        """
        ts = 1705176162
        formated_ts = datetime.fromtimestamp(ts)
        cell = Cell("cell_9", "", 1, 1, False, None)
        cell.save()
        TEROSData.add_teros_data("cell_9", formated_ts, 0.42, 2, 3, 4, 5)
    
        teros_data_obj = TEROSData.get_teros_data_obj(
            cell.id, "none", formated_ts, formated_ts, False
        )
    
        assert 42 in teros_data_obj["vwc"]
>       assert teros_data_obj["vwc_unit"] == "%"
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
E       KeyError: 'vwc_unit'

tests/test_teros_data.py:199: KeyError