fix: osnap snapshot tx builder bug

[daywiss]

Summary

There was a bug in the transaction builder where the app would load all tokens you have balances for (your safe on a certain network), then when you switch safes, that list of tokens would not update. We also were not including the balance of the native token in the token chooser modal. This was because the balance pulled from gnosis, if that balance was for a native token it would be stripped out by the app, then later we just hardcoded in the native asset for the chain as an option, but without the balance info.

This PR rectifies some of the state management so that we reload token balances and token lists when we switch safes.
It also ensures we keep the safe's balance for native tokens so we can display this data to the user.

How to test

1. go to an osnap plugin enabled space
2. create a proposal, in the transactiion builder select send tokens
3. see that safe assets show up in the assets list