Update AuthRequest event to carry either signature or TX summary

[bobbinth]

This PR changes the structure of the AuthRequest event from:

AuthRequest {
    pub_key_commitment: PublicKeyCommitment,
    tx_summary: Option<TransactionSummary>,
    signature: Option<Vec<Felt>>,
}

To

AuthRequest {
    pub_key_commitment: PublicKeyCommitment,
    tx_summary_or_signature: TxSummaryOrSignature,
}

The intent here is to make it so that when a signature for a given message is already present in the advice provider, we do not require constructing the TX summary matching the specified message. This allows the code to verify signatures over arbitrary messages.

For more context see #3044 (comment).

[PhilippGackstatter]

Looks good!

[onurinanc]

Looks good! Thank you!