Fix PytestAssertRewriteWarning for credentials fixture module

[adamtheturtle]

Move tests.mock_vws.fixtures.credentials first in pytest_plugins so pytest registers it for assertion rewriting before other fixture modules (prepared_requests, vuforia_backends) import it as a side effect, which was causing a PytestAssertRewriteWarning.

---

Note

Low Risk
Test-only change that adjusts plugin import order and adds comments; low risk aside from potential fixture import-order assumptions.

Overview
Reorders pytest_plugins in tests/conftest.py so tests.mock_vws.fixtures.credentials is loaded before other fixture modules, and documents the reason.

This prevents a PytestAssertRewriteWarning by ensuring pytest registers credentials for assertion rewriting before it is imported as a side effect elsewhere.

^{Written by Cursor Bugbot for commit d295efa. This will update automatically on new commits. Configure here.}