feat: integrate nostrdb relay indexing

- Upgrade `nostrdb` to v0.6.1 with relay metadata support
- Switch to `nostr::RelayUrl` for typed relay URLs
- Use `process_event_with()` to pass relay info during ingestion
- Update `Relay`, `RelayPool`, and unknown ID logic accordingly

This enables richer indexing with relay provenance in events.

Signed-off-by: William Casarin <jb55@jb55.com>

crates/enostr/src/error.rs

@@ -25,6 +25,9 @@ pub enum Error {
     #[error("invalid public key")]
     InvalidPublicKey,
 
+    #[error("invalid relay url")]
+    InvalidRelayUrl,
+
     // Secp(secp256k1::Error),
     #[error("json error: {0}")]
     Json(#[from] serde_json::Error),