feat(dameng): full DM8 database support

Adds Dameng DM8 explain/autotrace support and user-management SQL support, with backend autotrace safety checks and escaped CREATE USER SQL.

crates/dbx-core/src/db_admin_sql.rs

@@ -144,6 +144,15 @@ pub fn build_duckdb_attach_database_sql(options: DuckDbAttachDatabaseSqlOptions)
     )
 }
 
+pub fn build_create_user_sql(username: &str, password: &str, tablespace: &str) -> String {
+    format!(
+        "CREATE USER {} IDENTIFIED BY {} DEFAULT TABLESPACE {};",
+        quote_table_identifier(Some(DatabaseType::Dameng), username),
+        quote_sql_string(password),
+        quote_table_identifier(Some(DatabaseType::Dameng), tablespace)
+    )
+}
+
 pub fn build_drop_object_sql(options: DropObjectSqlOptions) -> String {
     format!(
         "DROP {} {};",
@@ -492,6 +501,14 @@ mod tests {
         );
     }
 
+    #[test]
+    fn builds_dameng_create_user_sql_with_escaped_values() {
+        assert_eq!(
+            build_create_user_sql("app\"user", "pa'ss", "main\"space"),
+            "CREATE USER \"app\"\"user\" IDENTIFIED BY 'pa''ss' DEFAULT TABLESPACE \"main\"\"space\";"
+        );
+    }
+
     #[test]
     fn builds_drop_and_clear_table_sql() {
         let options = TableAdminSqlOptions {