tests(spanner): avoid table name collisions in tests

[chalmerlowe]

Fix Spanner Test Flakes: Avoid Generic Table Names

Problem

The sqlalchemy-spanner test suite occasionally fails with Duplicate name in schema: t. errors. This happens because multiple tests use the generic table name t. In a shared database environment, or due to buffered DDL statements in Spanner (which are non-transactional), a table from a previous test might still exist when a new test tries to create it.

Solution

Renamed the generic table name t to more specific names in several tests and fixtures to avoid collisions.

• In tests/conftest.py, renamed t to t_literal_round_trip_spanner.
• In tests/test_suite_14.py:
  • Renamed t to t_nullable_reflection in test_nullable_reflection.
  • Renamed t to t_type_round_trip in _type_round_trip.
  • Renamed t to t_percent_signs in EscapingTest.
  • Renamed t to t_do_numeric in NumericTest.

Notes to Reviewers

These changes are purely in test code and aim to improve test stability by eliminating shared resource name collisions.

[gemini-code-assist]

Code Review

This pull request reorganizes imports in test_suite_14.py and renames generic test table names (from "t" to more descriptive, unique names like "t_literal_round_trip_spanner", "t_nullable_reflection", etc.) across the test suite to prevent potential table name collisions. There are no review comments, so I have no feedback to provide.