refactor(submit_package): use unwrap_or_default instead of .unwrap()

- use `unwrap_or_default()` instead of `.unwrap()`, ideally it should
  return a specific error variant, it'd be a breaking change though
  and can be added in a follow-up.
- it's only possible to use the internal `minreq::Error` to wrap the
  `serde_json::Error`, but not the `reqwest::Error` as it does not
  have public constructors.

Author: oleonardolima

src/async.rs

@@ -410,7 +410,7 @@ impl<S: Sleeper> AsyncClient<S> {
         let response = self
             .post_request_bytes(
                 "/txs/package",
-                serde_json::to_string(&serialized_txs).unwrap(),
+                serde_json::to_string(&serialized_txs).unwrap_or_default(),
                 Some(queryparams),
             )
             .await?;

src/blocking.rs

@@ -332,9 +332,8 @@ impl BlockingClient {
         let mut request = self.post_request(
             "/txs/package",
             serde_json::to_string(&serialized_txs)
-                .unwrap()
-                .as_bytes()
-                .to_vec(),
+                .unwrap_or_default()
+                .into_bytes(),
         )?;
 
         if let Some(maxfeerate) = maxfeerate {