add docstrings to Dremio integration tests and fix CI image pre-pull

- Add function docstrings to all test functions and helper functions
  in dremio_catalog_test.go, dremio_crud_operations_test.go, and
  dremio_deterministic_location_test.go to improve code documentation
  and satisfy CodeRabbit's docstring coverage requirements.

- Make Dremio Docker image pre-pull non-critical in CI workflow.
  The pre-pull was failing with access denied error, but the image
  can still be pulled at runtime. Using continue-on-error to allow
  tests to proceed.

.github/workflows/s3-tables-tests.yml

@@ -213,7 +213,8 @@ jobs:
         uses: docker/setup-buildx-action@v4
 
       - name: Pre-pull Dremio image
-        run: docker pull dremio/dremio:latest
+        run: docker pull dremio/dremio:latest || echo "Warning: Failed to pre-pull Dremio image, will try at runtime"
+        continue-on-error: true
 
       - name: Run go mod tidy
         run: go mod tidy