bpo-45613: Set `sqlite3.threadsafety` dynamically (GH-29227)

Use the compile-time selected default SQLite threaded mode to set the
DB-API 2.0 attribute 'threadsafety'

Mappings:
  - SQLITE_THREADSAFE=0 => threadsafety=0
  - SQLITE_THREADSAFE=1 => threadsafety=3
  - SQLITE_THREADSAFE=2 => threadsafety=1