fix: use ESM export from index file

src/js/index.ts

@@ -1,6 +1,6 @@
-import * as signature from './signature';
 import * as asset from './asset';
 import * as keyDerivation from './key_derivation';
 import * as messageUtils from './message_utils';
 
-module.exports = {...signature, asset, keyDerivation, messageUtils};
+export {asset, keyDerivation, messageUtils};
+export * from './signature';