fix: infer type after isMultiaddr call (#227)

Give a hint to tsc that the value is a multiaddr.

src/index.ts

@@ -552,7 +552,7 @@ export class Multiaddr {
   /**
    * Check if object is a CID instance
    */
-  static isMultiaddr (value: any) {
+  static isMultiaddr (value: any): value is Multiaddr {
     return value instanceof Multiaddr ?? Boolean(value?.[symbol])
   }