test(spanner): consolidate admin system tests to reduce DDL and database churn

Consolidate administrative system tests in `test_database_api.py` to eliminate
redundant database creations, long-running operations (LROs), and schema churn:
1. Consolidate Create & Update Tests:
   - Combine PITR database creation and subsequent DDL update into a single
     test (`test_create_and_update_database_pitr`), asserting both client
     properties and Information Schema catalog values.
   - Combine default leader creation and subsequent update into a single
     multi-region database test (`test_create_and_update_database_with_default_leader`).
   - Merge `test_update_ddl_w_operation_id` into `test_create_database_and_update_ddl`.
2. Consolidate Database Roles & Permissions:
   - Merge `test_create_role_grant_access_success` and `test_list_database_role_success`
     into `test_create_role_grant_access_and_list_roles`.
   - Strip the 20-table schema down to only the single required table (`contacts`).
   - Eliminate redundant teardown DDL (revoking permissions and dropping roles)
     immediately prior to database deletion.
   - Fix a lazy evaluation bug where the parent role query was never iterated
     and therefore never dispatched over the wire.
3. Remove Pure Server-Side DDL Parser Tests:
   - Drop `test_create_database_pitr_invalid_retention_period` and
     `test_update_ddl_w_pitr_invalid`, which tested Spanner backend syntax
     rejection of '0d' rather than client validation logic.
4. Fix Multi-Region Database Timeout:
   - Replace the hardcoded 30-second timeout on multi-region database creation
     with `DBAPI_OPERATION_TIMEOUT` (240s) to prevent CI flakes under load.

Savings:
- Eliminates 5 full database creations and drops (including 1 multi-region DB).
- Eliminates ~8 long-running DDL operations.

Author: olavloite