Add ErrorKind::DeserializeError to specialize ErrorKind::Message (extract::path::ErrorKind) (#2720)

This commit introduces another `extract::path::ErrorKind` variant that captures the
serde error nominally captured through the `serde::de::Error` trait impl on `PathDeserializeError`.
We augment the deserialization error with the captured (key, value), allowing `extract::Path`, and wrapping
extractors, to gain programmatic access to the key name, and attempted deserialized value.

The `PathDeserializationError::custom` is used two places in addition to capture the deserialization error.
These usages should still be unaffected.

Co-authored-by: David Mládek <[email protected]>

axum-extra/src/extract/optional_path.rs

@@ -94,7 +94,7 @@ mod tests {
         let res = client.get("/NaN").await;
         assert_eq!(
             res.text().await,
-            "Invalid URL: Cannot parse `\"NaN\"` to a `u32`"
+            "Invalid URL: Cannot parse `NaN` to a `u32`"
         );
     }
 }