Node: Force nominal typing for zkgroup ByteArray subclasses

Without this, two ByteArray types without any additional operations
are structurally equivalent, and so TypeScript permits passing one as
the other. (Thanks, Fedor!)

node/ts/zkgroup/profiles/ProfileKeyCommitment.ts

@@ -7,6 +7,8 @@ import ByteArray from '../internal/ByteArray';
 import * as Native from '../../../Native';
 
 export default class ProfileKeyCommitment extends ByteArray {
+  private readonly __type?: never;
+
   constructor(contents: Buffer) {
     super(contents, Native.ProfileKeyCommitment_CheckValidContents);
   }