refactor!: Use SerializationError for too long messages

This will allow merging the `SendError` and `RecvError` types.

BREAKING CHANGE: The `SendError::TooLong` variant has been removed. The
same condition (attempting to send a message longer than `u32::MAX`
bytes) will now return `SendError::Serialization`.

src/error.rs

@@ -301,11 +301,7 @@ pub enum SendError {
     /// Limitations in the serde API mean we cannot verify this statically, and we don't want to
     /// introduce potential panics.
     #[error("Failed to serialize message")]
-    Serialization(#[source] SerializationError),
-
-    /// The serialized message is too long (max: 4 GiB).
-    #[error("The serialized message is too long ({0} bytes, max: 4 GiB)")]
-    TooLong(usize),
+    Serialization(#[from] SerializationError),
 
     /// Connection was lost when trying to send a message.
     #[error("Connection was lost when trying to send a message")]

src/wire_msg.rs

@@ -127,7 +127,11 @@ struct MsgHeader {
 impl MsgHeader {
     fn new(msg: &Bytes, usr_msg_flag: u8) -> Result<Self, SendError> {
         match u32::try_from(msg.len()) {
-            Err(_) => Err(SendError::TooLong(msg.len())),
+            Err(_) => Err(SerializationError::new(format!(
+                "The serialized message is too long ({} bytes, max: 4 GiB)",
+                msg.len()
+            ))
+            .into()),
             Ok(data_len) => Ok(Self {
                 version: MSG_PROTOCOL_VERSION,
                 data_len,