Nostr Wallet Connect (NWC) describes a way for clients to access a remote Lightning wallet through a standardized protocol. This allows users to make payments directly in the Nostr client app without switching context when opening another wallet.

Alby, Mutiny, Umbrel are wallets which already support NWC.
Amethyst, Damus, Primal and Nostur can servce as examples how the UI for NWC could look like.

NIP-47 spec: https://github.com/nostr-protocol/nips/blob/master/47.md
Alby SDK for clients (only JS): https://github.com/getAlby/alby-js-sdk#nostr-wallet-connect-documentation

I'd recommend switching from k256 to secp256k1 because the library using C bindings to the same library used by Bitcoin Core are much faster, is better maintained, and it still compiles to wasm, since we also use it in BDK and RGB. I discovered k256 was much slower when I went to try it out for the Rana Nostr vanity key generator. If you're curious and want to see for yourself the difference, try this branch:
grunch/rana@main...cryptoquick:rana:perf-k256

Stripping trailing slashes seems like a bug. In gossip, if I add a relay like wss://some.host/path/, the trailing slash gets stripped (which can be a problem if the server doesn't respond to both URLs), and then the NIP-11 request fails because it actually requests https://some.host/. I think slashes in the path of a url should always be preserved.

Would it be possible to add the #nostr tag to this repo I'll show up in this nice list here: https://github.com/topics/nostr

What do you thing of separating moving the types into a sub crate with the types separated from the binary? This would let other projects use the types without the larger dependencies of the binary, specifically reqwest and tungstenite which are not necessarily needed depending on what the other project is doing.