EIP-161: Sending zero to an empty account

## Observation

EIP-161 says:

> An account is considered to be touched when it is involved in any potentially state-changing operation. This includes, but is not limited to, being the recipient of a **transfer of zero value**.

The specs seem to diverge from the clients and the EIP here, it seems to not be testable because empty accounts are not allowed in the pre-state.

## Expectation

I would have expected that when we transfer 0 to an account, that there would be some check like:

```
if account_exists_and_is_empty(tx_state, target): destroy_account(...)
```

or

```
modify_state(..., lambda _: None)
```

To signal the account has been touched and should be removed.

The code currently checks for value != 0 when sending, so without such checks we would not mark an account as touched.

(Not sure about removing the value != 0 check since that potentially affects BAL)

The issue points to the transfer path's value != 0 check; start there and compare its account-touch behavior with EIP-161 and client behavior. Verify whether the current pre-state and tests can represent an empty recipient. Done when the specification's expected zero-value behavior is resolved and covered by a test or documented evidence.

Written by the indexing model from the issue text.