audit: H-02 Votes Can Be Blocked

[Orland0x]

The StarknetCommit contract allows anyone to submit a hash representing their vote,
which will be recorded with their L1 address in the EthTxAuthenticator contract. Later,
they can consume the commitment, provided the hash matches a valid transaction (i.e.,
proposal, vote, or proposal update) from the original sender.
However, an attacker can submit a hash corresponding to another user's valid transaction. This
will prevent the victim from making the same commitment to execute the transaction.
Fortunately, since metadata_uri is a free parameter, they could commit to an equivalent
transaction with a different metadata_uri value, and use a private relayer to ensure they
cannot be front-run.
Consider including the L1 message sender as part of the hash commitment to ensure
uniqueness. Alternatively, consider using a two-dimensional storage mapping to allow multiple
users to commit to the same hash.