perf(postgres-driver): build user defined types map in linear time (#11586)

`loadUserDefinedTypes` built its oid -> typname map with a reduce that
spread the accumulator on every row, copying the whole map n times. That
is quadratic and fully synchronous, so it blocks the event loop.

This went unnoticed while the query only selected `typcategory in ('U', 'E')`
(~20 rows on a stock Postgres). #11149 added `'A'` so that array-typed
columns get mapped, and Postgres auto-creates an array type for every
relation — the row count now scales with the number of tables in the
database, not with the number of actual user defined types.

Measured on postgres:16, `SELECT count(*) FROM pg_type WHERE typcategory
in ('U', 'E', 'A')`:

| tables in database | rows | spread reduce | in-place loop |
| ------------------ | ---- | ------------- | ------------- |
| 0                  |  313 |        6.3 ms |       0.12 ms |
| 5000               | 5313 |       2355 ms |       0.45 ms |
| ~20000             |   -  |      35116 ms |       1.10 ms |

Author: ovr

packages/cubejs-postgres-driver/src/PostgresDriver.ts

@@ -315,10 +315,13 @@ export class PostgresDriver<Config extends PostgresDriverConfiguration = Postgre
         []
       );
 
-      this.userDefinedTypes = customTypes.rows.reduce(
-        (prev, current) => ({ [current.oid]: current.typname, ...prev }),
-        {}
-      );
+      const userDefinedTypes: Record<string, string> = {};
+
+      for (const row of customTypes.rows) {
+        userDefinedTypes[row.oid] = row.typname;
+      }
+
+      this.userDefinedTypes = userDefinedTypes;
     }
   }