feat: rewrite the nip-4e implementation (#1)

Make NIP-4e a core feature, not an optional feature.

Note:
- The UI is broken and needs to be updated in a separate PR.

Reviewed-on: #1

crates/chat_ui/src/actions.rs

@@ -1,4 +1,3 @@
-use encryption::SignerKind;
 use gpui::Action;
 use nostr_sdk::prelude::*;
 use serde::Deserialize;
@@ -7,10 +6,6 @@ use serde::Deserialize;
 #[action(namespace = chat, no_json)]
 pub struct SeenOn(pub EventId);
 
-#[derive(Action, Clone, PartialEq, Eq, Deserialize)]
-#[action(namespace = chat, no_json)]
-pub struct SetSigner(pub SignerKind);
-
 /// Define a open public key action
 #[derive(Action, Clone, PartialEq, Eq, Deserialize, Debug)]
 #[action(namespace = pubkey, no_json)]