Add PostgreSQL version of SQLite integ tests

- Add PostgreSQL throwaway database
- Add optional length parameter for random string
- Fix syntax for PostgreSQL in several areas
- Add optional ID for whereById type determination

src/Query/Exists.php

@@ -25,12 +25,13 @@ class Exists
      * Query to determine if a document exists for the given ID
      *
      * @param string $tableName The name of the table in which document existence should be checked
+     * @param mixed $docId The ID of the document whose existence should be checked (optional; string ID assumed)
      * @return string The query to determine document existence by ID
      * @throws DocumentException If the database mode has not been set
      */
-    public static function byId(string $tableName): string
+    public static function byId(string $tableName, mixed $docId = null): string
     {
-        return self::query($tableName, Query::whereById());
+        return self::query($tableName, Query::whereById(docId: $docId));
     }
 
     /**