feat(entity): add GlobalConstantDef class for namespace constant metadata

- Create GlobalConstantDef entity to store namespace/global constant metadata
- Add properties for type, codegenFinalized, initialization code, and name
- Include constructor with parameters for value expression and source details
- Implement metadata collection during preprocessing functionality

src/Entity/GlobalConstantDef.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace TypePhp\Entity;
+
+use PhpParser\Node;
+
+/** Metadata for a namespace/global constant collected during preprocessing. */
+final class GlobalConstantDef
+{
+    public string $type;
+    public bool $codegenFinalized;
+    public string $initializationCode = '';
+    public string $afterInitializationCode = '';
+
+    public function __construct(
+        public string $name,
+        public string $value,
+        public ?Node\Expr $valueExpr,
+        public string $namespace,
+        public string $sourceFile,
+        string $type,
+        bool $codegenFinalized,
+    ) {
+        $this->type = $type;
+        $this->codegenFinalized = $codegenFinalized;
+    }
+}