*: Don't leak prost dependency in error types (#3058)

With the current design, a major version bump of `prost` leaks into
all consumers of `prost-codec`.

protocols/dcutr/src/protocol/inbound.rs

@@ -118,12 +118,8 @@ impl PendingConnect {
 
 #[derive(Debug, Error)]
 pub enum UpgradeError {
-    #[error("Failed to encode or decode")]
-    Codec(
-        #[from]
-        #[source]
-        prost_codec::Error,
-    ),
+    #[error(transparent)]
+    Codec(#[from] prost_codec::Error),
     #[error("Stream closed")]
     StreamClosed,
     #[error("Expected at least one address in reservation.")]

protocols/dcutr/src/protocol/outbound.rs

@@ -116,12 +116,8 @@ pub struct Connect {
 
 #[derive(Debug, Error)]
 pub enum UpgradeError {
-    #[error("Failed to encode or decode: {0}")]
-    Codec(
-        #[from]
-        #[source]
-        prost_codec::Error,
-    ),
+    #[error(transparent)]
+    Codec(#[from] prost_codec::Error),
     #[error("Stream closed")]
     StreamClosed,
     #[error("Expected 'status' field to be set.")]