feat: add ReissueRequestBuilder to simplify aggregating dbc ownership proofs

[dan-da]

So now creating a ReissueRequest can look something like:

        let rr = ReissueRequestBuilder::new(reissue_tx);
            .add_dbc_signer(
                genesis_dbc.name(),
                genesis_owner.public_key_set,
                genesis_owner.index,
                genesis_owner.secret_key_share,
            )
            .build()?;

or for a more complicated case with multiple input dbcs and 2 signers for each:

let owner_shares = vec![(0, share0),(1, share1)];
let mut builder = ReissueRequestBuilder::new(reissue_tx.clone());
for dbc in reissue_tx.inputs.iter() {
    builder.add_dbc_signers(
        dbc.name(),
        owner.public_key_set,
        owner_shares
    );
}
let reissue_request = builder.build()?;

[dan-da]

cleanup: closing out-dated PRs.