Add addCount, addFirst, addMax, and addMin functions

Signed-off-by: David Arendsen <darendsen@gamepoint.com>

tests/Functions/CountFunctionTest.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Functions;
+
+use Arendsen\FluxQueryBuilder\Functions\Count;
+use PHPUnit\Framework\TestCase;
+
+final class CountFunctionTest extends TestCase
+{
+    public function testSimpleCount()
+    {
+        $expression = new Count();
+
+        $query = '|> count() ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+
+    public function testCountWithColumn()
+    {
+        $expression = new Count('_value');
+
+        $query = '|> count(column: "_value") ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+}