fix(env): resolve PHPStan “left side of ?? is not nullable” for getenv()

Normalized getenv() handling to convert its false return value into null, ensuring the expression becomes nullable as required by PHPStan.

Updated the environment resolution chain to use an explicit ternary for getenv() so the final ?? $default fallback remains valid.

Fully resolves PHPStan warning:
“Expression on left side of ?? is not nullable.”

Author: megyptm

src/Helpers/EnvHelper.php

@@ -84,8 +84,8 @@ public static function get(string $key, mixed $default = null): mixed
 
         // 🔍 Search through multiple sources
         $value = $_ENV[$key]
-                 ?? $_SERVER[$key]
-                    ?? getenv($key)
+                 ?? ($_SERVER[$key] ?? null)
+                    ?? (($env = getenv($key)) !== false ? $env : null)
                        ?? $default;
 
         // 🧠 Cache the resolved value for future requests