[Bitcoin/Rust] Add support for creating Ordinal NFT inscriptions

[lamafab]

This PR allows you to create Ordinal NFT inscriptions, example: https://www.blockchain.com/explorer/transactions/btc/173f8350b722243d44cc8db5584de76b432eb6d0888d9e66e662db51584f44ac

Generally ready, two things to consider:

1. The TransactionVariant protobuf enum now has the variants:

enum TransactionVariant {
    P2PKH = 0;
    P2WPKH = 1;
    P2TRKEYPATH = 2;
    BRC20TRANSFER = 3;
    NFTINSCRIPTION = 4;
}

The last two can technically be combined, I propose calling it P2ScriptPath (P2TRKEYPATH should be lowercased, too). But that's a breaking change afaik.

EDIT: We're keeping it like this now, we're planning on writing a new interface as part of a larger task anyway.

2. Would be nice if someone could quickly write Script::buildNftInscription in src/Bitcoin.cpp in order to expose it. Note that one has to pass on the MimeType from src/nft.rs. Done

EDIT: Additionally, added tests for C++ and Swift, Kotlin is WIP... having some build/dependency error (?). Will change this from Draft to Open, let the CI run.

[satoshiotomakan]

Good job! Just a few questions/suggestions/reminders

[lamafab]

@satoshiotomakan finally :) done

[satoshiotomakan]

LGTM 🔥