Add silentpayments logic

[Sosthene00]

I needed to parse Silent Payments address inscribed in DNS record according to the BIP353 specification, I think that's rather straightforward the only thing I'm not quite sure of is support for testnet/signet sp addresses. Opening it as a draft for now

[TheBlueMatt]

Hmm, what's the status of upstreaming address parsing into rust-bitcoin? I presume it could be upstreamed without support for broader SP payment support to get it done here.

I'm not super excited about adding hex, serde, serde-json, and bimap (which appears to be a single-developer crate) to the transitive dependency set, and I'm not clear on how many wallets will actually support silent payments until it's upstreamed anyway.

[TheBlueMatt]

GitHub won't let me comment on the diff (man it's gone to shit) but you should maybe also handle req-sp, I imagine? Though the semantics of that are maybe somewhat ill-defined if it's not the only address (I guess it means "you have to support parsing this but you can choose to not use it"?)

[Sosthene00]

Thanks for your quick feedback, I'll try to answer each point as best as I can:

what's the status of upstreaming address parsing into rust-bitcoin?

I took a look and afaict it hasn't been moving for a while and I don't think there's anything usable by now.

I'm not super excited about adding hex, serde, serde-json, and bimap (which appears to be a single-developer crate) to the transitive dependency set

Yes totally agree, as a temporary solution waiting for upstream address parsing in rust-bitcoin I can try to rethink how things are done in rust-silentpayments to reduce transitive dependencies at bare minimum?

you should maybe also handle req-sp, I imagine?

Yes actually to be honest I was indeed a little confused about that, so I decided to let it aside. I think if we signal a silent payment address in payment instructions we are unlikely to add a static fallback address anyway, but that would be totally possible and legitimate to have both sp and lno, but then we shouldn't make any of them req?