Introduce subscription support in the Wallet crate.

The main goal is to add a subscription to CDK Mint updates into the wallet.
This feature will be particularly useful for improving the code whenever loops
hit the mint server to check status changes.

The goal is to add an easy-to-use interface that will hide the fact that we're
connecting to WebSocket and subscribing to events. This will also hide the fact
that the CDK-mint server may not support WebSocket updates.

To be fully backward compatible, the HttpClientMethods traits have a new
method, `subscribe,` which will return an object that implements
`ActiveSubscription.`

In the primary implementation, there is a `SubscriptionClient` that will
attempt to connect through WebSocket and will fall to the HTTP-status pull and
sleep approach (the current approach), but upper stream code will receive
updates as if they come from a stream of updates through WebSocket. This
`SubscriptionClient` struct will also manage reconnections to WebSockets (with
automatic resubscriptions) and all the low-level stuff, providing an
easy-to-use interface and leaving the upper-level code with a nice interface
that is hard to misuse. When `ActiveSubscription` is dropped, it will
automatically unsubscribe.

Fixed bug with Default as described in https://github.com/cashubtc/cdk/pull/473#discussion_r1871032297

crates/cdk-integration-tests/src/lib.rs

@@ -1,7 +1,6 @@
 use std::collections::{HashMap, HashSet};
 use std::str::FromStr;
 use std::sync::Arc;
-use std::time::Duration;
 
 use anyhow::{bail, Result};
 use axum::Router;
@@ -12,17 +11,19 @@ use cdk::cdk_lightning::MintLightning;
 use cdk::dhke::construct_proofs;
 use cdk::mint::FeeReserve;
 use cdk::mint_url::MintUrl;
+use cdk::nuts::nut17::Params;
 use cdk::nuts::{
     CurrencyUnit, Id, KeySet, MintBolt11Request, MintInfo, MintQuoteBolt11Request, MintQuoteState,
-    Nuts, PaymentMethod, PreMintSecrets, Proofs, State,
+    NotificationPayload, Nuts, PaymentMethod, PreMintSecrets, Proofs, State,
 };
 use cdk::types::{LnKey, QuoteTTL};
 use cdk::wallet::client::{HttpClient, MintConnector};
+use cdk::wallet::subscription::SubscriptionManager;
+use cdk::wallet::WalletSubscription;
 use cdk::{Mint, Wallet};
 use cdk_fake_wallet::FakeWallet;
 use init_regtest::{get_mint_addr, get_mint_port, get_mint_url};
 use tokio::sync::Notify;
-use tokio::time::sleep;
 use tower_http::cors::CorsLayer;
 
 pub mod init_fake_wallet;
@@ -129,15 +130,18 @@ pub async fn wallet_mint(
 ) -> Result<()> {
     let quote = wallet.mint_quote(amount, description).await?;
 
-    loop {
-        let status = wallet.mint_quote_state(&quote.id).await?;
+    let mut subscription = wallet
+        .subscribe(WalletSubscription::Bolt11MintQuoteState(vec![quote
+            .id
+            .clone()]))
+        .await;
 
-        if status.state == MintQuoteState::Paid {
-            break;
+    while let Some(msg) = subscription.recv().await {
+        if let NotificationPayload::MintQuoteBolt11Response(response) = msg {
+            if response.state == MintQuoteState::Paid {
+                break;
+            }
         }
-        println!("{:?}", status);
-
-        sleep(Duration::from_secs(2)).await;
     }
 
     let receive_amount = wallet.mint(&quote.id, split_target, None).await?;
@@ -169,17 +173,25 @@ pub async fn mint_proofs(
 
     println!("Please pay: {}", mint_quote.request);
 
-    loop {
-        let status = wallet_client
-            .get_mint_quote_status(&mint_quote.quote)
-            .await?;
+    let subscription_client = SubscriptionManager::new(Arc::new(wallet_client.clone()));
 
-        if status.state == MintQuoteState::Paid {
-            break;
+    let mut subscription = subscription_client
+        .subscribe(
+            mint_url.parse()?,
+            Params {
+                filters: vec![mint_quote.quote.clone()],
+                kind: cdk::nuts::nut17::Kind::Bolt11MintQuote,
+                id: "sub".into(),
+            },
+        )
+        .await;
+
+    while let Some(msg) = subscription.recv().await {
+        if let NotificationPayload::MintQuoteBolt11Response(response) = msg {
+            if response.state == MintQuoteState::Paid {
+                break;
+            }
         }
-        println!("{:?}", status.state);
-
-        sleep(Duration::from_secs(2)).await;
     }
 
     let premint_secrets = PreMintSecrets::random(keyset_id, amount, &SplitTarget::default())?;