feat: add function to prepopulate account number cache (#254)

motivation:
- in FE, when creating the first transaction (e.g. placing a short term
order after web app starts), we need to query account as part of the tx
to get the account number before sending the place order message.
- we can actually pre populate the account number cache earlier (i.e.
app starts / clients initialized with address) so it doesn't have to be
a blocker
- once timestamp nonce is enabled, we will no longer need to fetch
account seq number, so this will also help eliminate the round trip time
blocker when placing a stateful order first

change:
- add `populateAccountNumberCache` function

testing:
- tested locally / integration with FE app
dydxprotocol/v4-web#1062
- backwards compatible