Parallelize fetching token-details

[piyalbasu]

When we fetch details about a SEP-41 custom token, we need to get multiple pieces of information: balance, decimals, name, and symbol. Currently, we make these requests sequentially. If we were to make these calls in parallel, rather than waiting for 4 separate XHR’s to complete, we would just be left waiting for the longest of the 4 XHR’s to complete. For additional context, we’ve heard that not many users have custom tokens, so this may be an optimization that only meaningfully helps a small number of users.