refactor(generator): 优化类型声明关键字生成逻辑

- 将条件判断语句替换为 switch 表达式以提高可读性
- 添加对 partial interface 类型的支持
- 为不支持的类型添加异常处理机制
- 简化代码结构并提升维护性

GFramework.Godot.SourceGenerators/Registration/AutoRegisterExportedCollectionsGenerator.cs

@@ -491,11 +491,15 @@ public sealed class AutoRegisterExportedCollectionsGenerator : IIncrementalGener
 
     private static string GetTypeDeclarationKeyword(INamedTypeSymbol typeSymbol)
     {
-        return typeSymbol.IsRecord
+        return typeSymbol switch
-            ? typeSymbol.TypeKind == TypeKind.Struct ? "partial record struct" : "partial record"
+        {
-            : typeSymbol.TypeKind == TypeKind.Struct
+            { IsRecord: true, TypeKind: TypeKind.Struct } => "partial record struct",
-                ? "partial struct"
+            { IsRecord: true } => "partial record",
-                : "partial class";
+            { TypeKind: TypeKind.Struct } => "partial struct",
+            { TypeKind: TypeKind.Class } => "partial class",
+            { TypeKind: TypeKind.Interface } => "partial interface",
+            _ => throw new NotSupportedException($"Unsupported type: {typeSymbol.TypeKind}")
+        };
     }
 
     private static string GetTypeDeclarationName(INamedTypeSymbol typeSymbol)