Support async sql.js initialization for ATTACH SQLITE DATABASE

[Copilot]

ATTACH SQLITE DATABASE assumed SQL.Database was immediately available, which breaks in browser setups using modern sql.js async initialization. This caused ATTACH/USE/SELECT flows to fail with TypeError: SQL.Database is not a constructor.

• SQLite adapter

  • Resolve sql.js from either:
    • a ready SQL.Database module, or
    • an async initializer exposed as SQL or initSqlJs
  • Cache successful initialization for reuse
  • Validate that the initialized module actually exposes Database

• Async error handling

  • Reject cleanly when sql.js initialization fails
  • Reject cleanly when the SQLite file cannot be loaded
  • Clear failed initialization state so a later retry can succeed if the environment is corrected

• Regression coverage

  • Add focused coverage for:
    • async sql.js initialization
    • browser-style initSqlJs
    • invalid sql.js module shape
    • initialization failure and retry
    • file-load failure

await alasql([
  'ATTACH SQLITE DATABASE inscriptions("mydb.sqlite3")',
  'USE inscriptions',
  'SELECT * FROM signatures',
]);

• Fixes alasql.js:19270 Uncaught TypeError: SQL.Database is not a constructor #1284