test(python): cover namespace operations without pylance (#4174)

The "Test without pylance or pandas" CI job only ran `test_table.py`, so
the
regression fixed in #3606 had no guard: sync namespace operations used
to route
through the Python `lance_namespace` client, whose `dir` implementation
ships in
the optional `pylance` extra, so
`lancedb.connect(path).list_namespaces()` failed
with `No module named 'lance'` while the async API worked.

Adds `python/python/tests/test_namespace_no_pylance.py` and runs it in
that
job. Its `without_pylance` fixture blocks `lance` imports, so the guard
also
fires in environments that do have `pylance` installed. Coverage: the
original
reproducer, nested namespace lifecycle, namespaced and root table
lifecycle, the
async path, and the one API that legitimately still needs `pylance`
(`namespace_client()`).

Verified the guard actually catches the regression: against
`lancedb==0.33.0`,
three of these tests fail with the original error; against a fixed build
all
pass.

Co-authored-by: Xuanwo <github@xuanwo.io>

.github/workflows/python.yml

@@ -156,7 +156,7 @@ jobs:
       - name: Test without pylance or pandas
         run: |
           pip uninstall -y pylance pandas
-          pytest -vv python/tests/test_table.py
+          pytest -vv python/tests/test_table.py python/tests/test_namespace_no_pylance.py
       # Make sure wheels are not included in the Rust cache
       - name: Delete wheels
         run: rm -rf target/wheels