Return parsed token accounts in simulateBundle

[mcintyre94]

Problem

If you call simulateBundle and pass a token account in pre/postExecutionAccountsConfigs, then the token accounts are never returned in JSON. You will always get the base64 encoded data.

This is caused by attempting to encode the data without fetching the number of decimals for the mint, which causes a fallback to base64 data.

This was fixed for simulateTransaction upstream, but simulateBundle has the same issue.

Upstream issue (with more details of the code path causing this): solana-labs/solana#34693
Upstream fix to simulateTransaction: solana-labs/solana#34619

Summary of Changes

The changes are based on the upstream changes in simulateTransaction.

Instead of directly encoding the post-account data, we call get_encoded_account (added in the upstream PR), which will correctly parse a token account. As this function was written for transaction post-accounts it also takes overwrite_accounts: Option<&HashMap<Pubkey, AccountSharedData>>, so that account state can be overridden if a transaction has changed it.

In order to provide this, we now maintain a AccountOverrides object in simulateBundle. This is the same data structure, but has some useful helper functions and I think makes sense to use here. After each transaction, this is updated (using upsert_account_overrides) with the post_accounts from the transaction. This is then passed when we encode the post-accounts for that transaction.

The result is that simulateBundle now correctly JSON encodes token accounts, using data from the transactions, or the bank if required.

[mcintyre94]

Closing, superseded by #600