test: consolidate adapter contract matrices

[cofin]

Summary

• consolidate repeated adapter storage, exception, EXPLAIN, migration, event queue, Arrow, parameter-style, and driver-basics coverage into capability contract modules
• remove generic adapter-local files now represented by the contract matrix
• update the RustFS fixture contract scan to follow the consolidated storage bridge test

Verification

• uv run pytest tests/integration/adapters/contracts/test_parameter_styles.py tests/integration/adapters/contracts/test_driver_basics.py tests/integration/adapters/contracts/test_arrow.py tests/integration/adapters/contracts/test_event_queue.py -q -m "sqlite or duckdb": 15 passed
• uv run pytest tests/integration/adapters/contracts/test_storage_bridge.py tests/integration/adapters/contracts/test_exceptions.py tests/integration/adapters/contracts/test_explain.py tests/integration/adapters/contracts/test_migrations.py -q -k "sqlite or duckdb": 75 passed
• uv run pytest tests/integration/adapters/contracts --collect-only -q: 8 files / 370 items
• uv run pytest tests/integration/adapters --collect-only -q: 163 files / 2167 items
• uv run pytest tests/integration/test_rustfs_fixture_contract.py -q: 2 passed
• uv run pytest tests/unit/loader/test_loading_patterns.py::test_large_fixture_loading_performance -q: 1 passed
• uv run pytest tests/integration/adapters/cockroach_asyncpg/test_driver.py::test_cockroach_asyncpg_basic_crud -q: 1 passed
• uv run pytest tests/integration/adapters/contracts/test_driver_basics.py::test_driver_basic_operations[cockroach-asyncpg] tests/integration/adapters/contracts/test_parameter_styles.py::test_adapter_parameter_style_executes[cockroach-asyncpg-numeric] -q: 2 passed
• uv run pytest tests/integration/storage/test_integration.py tests/integration/storage/test_signing.py -q: 54 passed
• make lint: passed

make test was run twice locally and is blocked by existing RootlessKit host-port allocation conflicts under xdist: CockroachDB/ParadeDB on one run and RustFS on the next. The CockroachDB blocker is tracked in Beads as sqlspec-zsc; the RustFS blocker is tracked as sqlspec-38nn.