Add queryTimeoutMs config option

[deepa0128]

What

Exposes a queryTimeoutMs option on both PostgresConfig and MysqlConfig.

Postgres — passes the value as statement_timeout to pg.Pool, which sets a PostgreSQL session-level statement_timeout. The database cancels any statement that exceeds the limit server-side.

MySQL — passes { sql, values, timeout } to mysql2's execute, which triggers a server-side KILL QUERY after the specified milliseconds. This uses mysql2's built-in mechanism, not a client-side race.

Usage

const db = createClient({
  dialect: 'postgres',
  // ...
  queryTimeoutMs: 5000, // cancel queries after 5 s
});

Stacks on #1.