Fallback to CoW RPCs when the wallet RPC is flaky

[kernelwhisperer]

Description
Providers like Brave Wallet fail to load balances, so we hardcoded this scenario to use our own RPCs fb18ee2

Proposal

1. Find a more elegant solution, detect if the rpc is flaky and not hardcode brave. (Other wallets could be failing too)
2. Collect 'Couldn't load balances' errors in sentry to keep an eye on them.