Add comprehensive Swift Package Manager tests

Add 24 tests covering:
- XCLocalSwiftPackageReference: create, getDisplayName, is()
- XCRemoteSwiftPackageReference: parsing, all 6 version requirement types
- XCSwiftPackageProductDependency: parsing, create with local/remote refs
- Round-trip serialization for all SPM types

Also fix XCSwiftPackageProductDependency.getObjectProps() to properly
declare `package` as a reference property, enabling automatic
inflation/deflation of package references.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: EvanBacon

src/api/XCSwiftPackageProductDependency.ts

@@ -29,7 +29,9 @@ export class XCSwiftPackageProductDependency extends AbstractObject<XCSwiftPacka
   }
 
   protected getObjectProps() {
-    return {};
+    return {
+      package: String,
+    };
   }
 
   getDisplayName(): string {