Bespoke constructor for `NonceMismatchError`

Not something that needs to be fixed now, but an idea for future improvement would be to:

```python
class NonceMismatchError(InvalidTransaction):
def __init__(self, account_nonce: Uint, tx_nonce: U256):
assert account_nonce != tx_nonce
if account_nonce > Uint(tx.nonce):
message = "nonce too low"
else:
message = "nonce too high"
super(message)

...
```

_Originally posted by @SamWilsn in https://github.com/ethereum/execution-specs/pull/1266#discussion_r2155240486_