Allow transcript labels to come from non-Rust code

[alinush]

Addresses dalek-cryptography#44.

This enables exporting a more versatile Bulletproof range proof verifier inside smart contracts (e.g., see Aptos and Sui).

Specifically, it allows smart contract developers to dynamically specify their domain separation tag (DST) in Transcript::new. This can be necessary in the smart contract setting where different smart contracts will verify proofs from different provers, each with an application-specific DST that might have been established years prior (e.g., think about verifying previously-computed Monero range proofs).

[gregnazario]

Hey @hdevalence could we get this reviewed and merged? Currently, any consumers using this patch have to apply it to themselves as well. Or is it @str4d who's the owner?

aptos-labs/aptos-core#9340

[gregnazario]

@hdevalence or @str4d could you take a look at this?

[gregnazario]

@hdevalence @str4d ?

[str4d]

This is not my crate; @hdevalence has the publish bit.

[hdevalence]

Hey, sorry about the delayed follow-up. As the history indicates, I haven't had capacity to maintain the crate. Happy to turn over maintenance and crates.io ownership to someone who does.

[alinush]

Hey, sorry about the delayed follow-up. As the history indicates, I haven't had capacity to maintain the crate. Happy to turn over maintenance and crates.io ownership to someone who does.

@hdevalence, I am happy to adopt responsibility for the crate. I DM'd you my email address on Telegram.

[HarryR]

This seems like an entirely sane easy merge PR.

Just press the button

[gregnazario]

@hdevalence @alinush let's get this pushed?

[HarryR]

Either that or we can just fork the repo, iirc hdv said he doesn't have time to maintain this any more.