refactor(l1): remove usage of assert_eq in frame decoding (rlpx) (#2456)

**Motivation**
Replaces `assert_eq` usage with proper errors in rlpx frame decoding
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**Description**
* Add error variant `RLPXError::InvalidMessageFrame`
* Remove usage of `assert_eq` in `RLPxCodec::decode` impl
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introduces -->

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes #1748

Author: fmoletta

crates/networking/p2p/rlpx/error.rs

@@ -49,6 +49,8 @@ pub(crate) enum RLPxError {
     MempoolError(#[from] MempoolError),
     #[error("Io Error: {0}")]
     IoError(#[from] std::io::Error),
+    #[error("Failed to decode message due to invalid frame: {0}")]
+    InvalidMessageFrame(String),
 }
 
 // tokio::sync::mpsc::error::SendError<Message> is too large to be part of the RLPxError enum directly

crates/networking/p2p/rlpx/frame.rs

@@ -113,9 +113,11 @@ impl Decoder for RLPxCodec {
                 .map_err(|_| RLPxError::CryptographyError("Invalid header mac".to_owned()))?,
         );
 
-        // TODO: replace these assert_eq! by actual errors
-        // https://github.com/lambdaclass/ethrex/issues/1748
-        assert_eq!(header_mac, expected_header_mac.0);
+        if header_mac != expected_header_mac.0 {
+            return Err(RLPxError::InvalidMessageFrame(
+                "Mismatched header mac".to_string(),
+            ));
+        }
 
         let header_text = header_ciphertext;
         // Use temporary value as it can be discarded if the buffer does not contain yet the full message
@@ -175,9 +177,11 @@ impl Decoder for RLPxCodec {
             .try_into()
             .map_err(|_| RLPxError::CryptographyError("Invalid frame mac".to_owned()))?;
 
-        // TODO: replace these assert_eq! by actual errors
-        // https://github.com/lambdaclass/ethrex/issues/1748
-        assert_eq!(frame_mac, expected_frame_mac);
+        if frame_mac != expected_frame_mac {
+            return Err(RLPxError::InvalidMessageFrame(
+                "Mismatched frame mac".to_string(),
+            ));
+        }
 
         // decrypt frame
         self.ingress_aes.apply_keystream(frame_ciphertext);