Add PostgreSQL Support (#3)

Reviewed-on: #3

tests/unit/Mapper/ExistsMapperTest.php

@@ -10,6 +10,7 @@ use PHPUnit\Framework\TestCase;
 /**
  * Unit tests for the ExistsMapper class
  */
+#[TestDox('Exists Mapper (Unit tests)')]
 class ExistsMapperTest extends TestCase
 {
     #[TestDox('Map succeeds for PostgreSQL')]