feat: enhance GenericVerifiableCredential interface with explicit optional properties

- Add name, description, and agent as optional properties to GenericVerifiableCredential
- Improve type safety and IntelliSense for common claim properties
- Maintain backward compatibility with existing code
- Reduce need for type assertions when accessing claim properties

src/interfaces/common.ts

@@ -2,6 +2,9 @@
 export interface GenericVerifiableCredential {
   "@context"?: string;
   "@type": string;
+  name?: string;
+  description?: string;
+  agent?: string;
   [key: string]: unknown;
 }