Ensure large >U32 is encoded as hex (#641)

* Ensure large >U32 is enocoded as hex

* Update U64 test compares to hex

* Update subscribe.spec.ts

packages/rpc-provider/src/mock/subscribe.spec.ts

@@ -39,7 +39,7 @@ describe('subscribe', () => {
 
   it('calls back with new headers', (done) => {
     return mock.subscribe('chain_newHead', 'chain_subscribeNewHead', (_: any, header: any) => {
-      if (header.number === 4) {
+      if (header.number === '0x0000000000000004') {
         done();
       }
     });
@@ -55,7 +55,7 @@ describe('subscribe', () => {
         throw new Error('testing');
       }
 
-      if (header.number === 3) {
+      if (header.number === '0x0000000000000003') {
         done();
       }
     });