refactor(mysql-connector): Enhance type safety for raw statements

Introduce a `RawStatement` interface to explicitly define the expected methods on the underlying database driver's statement object. This improves type safety and clarity within the `BoundableStatement` wrapper.

Also, make the `dialect` property's type a literal `'mysql'` to provide more precise type information.

Author: rrd108

src/runtime/server/utils/mysql-connector.ts

@@ -8,10 +8,16 @@ interface ConnectorOptions extends PoolOptions {
   database?: string
 }
 
+interface RawStatement {
+  all(...args: unknown[]): Promise<unknown[]>
+  run(...args: unknown[]): Promise<{ success: boolean }>
+  get(...args: unknown[]): Promise<unknown>
+}
+
 class BoundableStatement {
-  _statement: BoundableStatement | null
+  _statement: RawStatement | null
 
-  constructor(rawStmt: BoundableStatement | null) {
+  constructor(rawStmt: RawStatement | null) {
     this._statement = rawStmt
   }
 
@@ -105,7 +111,7 @@ export default function mysqlPoolConnector(opts: ConnectorOptions) {
 
   return {
     name: 'mysql',
-    dialect: 'mysql',
+    dialect: 'mysql' as const,
     getInstance: getPool,
     exec: (sql: string) => query(sql),
     prepare: (sql: string) => new StatementWrapper(sql, query),