Replace reqwest with simple-request

reqwest was replaced with hyper and hyper-rustls within monero-serai due to
reqwest *solely* offering a connection pool API. In the process, it was
demonstrated how quickly we can achieve equivalent functionality to reqwest for
our use cases with a fraction of the code.

This adds our own reqwest alternative to the tree, applying it to both
bitcoin-serai and message-queue. By doing so, bitcoin-serai decreases its tree
by 21 packages and the processor by 18. Cargo.lock decreases by 8 dependencies,
solely adding simple-request. Notably removed is openssl-sys and openssl.

One noted decrease functionality is the requirement on the system having
installed CA certificates. While we could fallback to the rustls certificates
if the system doesn't have any, that's blocked by
https://github.com/rustls/hyper-rustls/pulls/228.

message-queue/src/client.rs

@@ -11,7 +11,7 @@ use schnorr_signatures::SchnorrSignature;
 
 use serde::{Serialize, Deserialize};
 
-use reqwest::Client;
+use simple_request::{Request, Client};
 
 use serai_env as env;
 
@@ -45,7 +45,7 @@ impl MessageQueue {
       service,
       pub_key: Ristretto::generator() * priv_key.deref(),
       priv_key,
-      client: Client::new(),
+      client: Client::with_connection_pool(),
       url,
     }
   }
@@ -81,18 +81,30 @@ impl MessageQueue {
       id: u64,
     }
 
-    let res = loop {
+    let mut res = loop {
       // Make the request
       match self
         .client
-        .post(&self.url)
-        .json(&JsonRpcRequest { jsonrpc: "2.0", method, params: params.clone(), id: 0 })
-        .send()
+        .request(
+          Request::post(&self.url)
+            .header("Content-Type", "application/json")
+            .body(
+              serde_json::to_vec(&JsonRpcRequest {
+                jsonrpc: "2.0",
+                method,
+                params: params.clone(),
+                id: 0,
+              })
+              .unwrap()
+              .into(),
+            )
+            .unwrap(),
+        )
         .await
       {
         Ok(req) => {
           // Get the response
-          match req.text().await {
+          match req.body().await {
             Ok(res) => break res,
             Err(e) => {
               dbg!(e);
@@ -108,8 +120,8 @@ impl MessageQueue {
       tokio::time::sleep(core::time::Duration::from_secs(1)).await;
     };
 
-    let json =
-      serde_json::from_str::<serde_json::Value>(&res).expect("message-queue returned invalid JSON");
+    let json: serde_json::Value =
+      serde_json::from_reader(&mut res).expect("message-queue returned invalid JSON");
     if json.get("result").is_none() {
       panic!("call failed: {json}");
     }