*Make bls export an async wrapper to prevent top-level await

src/index.ts

@@ -4,11 +4,16 @@ import {getImplementation} from "./getImplementation.js";
 // Thanks https://github.com/iliakan/detect-node/blob/master/index.esm.js
 const isNode = Object.prototype.toString.call(typeof process !== "undefined" ? process : 0) === "[object process]";
 
+export const bls = async (): Promise<IBls> => {
   let bls: IBls;
+
   try {
     bls = await getImplementation(isNode ? "blst-native" : "herumi");
   } catch (e) {
     bls = await getImplementation("herumi");
   }
 
+  return bls;
+};
+
 export default bls;