ci: actually run pytest

The workflow is named "Tests" and has never run one — it installed ruff and
pyright, linted and type-checked tests/, and stopped there. tests/test_base_url.py
has existed since 0.3.x without ever executing in CI.

#18 asks for a fixture round-trip 'so model drift fails CI'. That only works if
the suite runs. Also fixes the pyright failure this PR surfaced: 'import pytest
could not be resolved', because the test extra was never installed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: root

.github/workflows/test.yml

@@ -22,11 +22,19 @@ jobs:
 
       - name: Install dependencies
         run: |
-          pip install -e ".[pandas]"
+          pip install -e ".[pandas,test]"
           pip install ruff pyright
 
       - name: Ruff check
         run: ruff check
 
       - name: Pyright
         run: pyright
+
+      # This workflow is named "Tests" but never ran any until now — `tests/` has
+      # existed since 0.3.x and CI only linted and type-checked it. #18 shipped two
+      # model/wire mismatches that a single parse of a real payload would have
+      # caught, so the fixture round-trip it asks for is only worth adding if it can
+      # actually fail the build.
+      - name: Pytest
+        run: pytest -q