Native fungible demo accepts 32-byte long address (linera-io#4599)

## Motivation

Fungible demo frontend accepted only 20-byte accounts.

## Proposal

Modify the regex to also accept 32-bytes (64 chars).

## Test Plan

Manual.

## Release Plan

This is a testnet branch. Updates fungible demo can be released from it.

## Links
Solves linera-io#4562
- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

Author: deuszx

examples/native-fungible/index.html

@@ -171,7 +171,7 @@ <h2>Chain history for <code id="chain-id" class="hex">requesting a new microchai
 
           let errors = [];
           try {
-              const match = recipient.match(/^(0x[0-9a-f]{40})@([0-9a-f]{64})$/);
+              const match = recipient.match(/^(0x[0-9a-f]{40}|0x[0-9a-f]{64})@([0-9a-f]{64})$/i);
               if (!match) throw new Error('Invalid recipient address: expected `owner@chain_id`');
 
               const query = gql(`mutation(