pub fn partial_sign(
pubkeys: impl IntoIterator<Item = PublicKey>,
agg_nonce: AggregatedNonce,
key: &Keypair,
sec_nonce: SecretNonce,
sighash: [u8; 32],
tweak: Option<[u8; 32]>,
other_sigs: Option<&[&PartialSignature]>,
) -> (PartialSignature, Option<Signature>)