`FromParts<Protocol>::Rejection` must implement `std::fmt::Display`.
Handlers can accept user-defined types if they implement
[FromParts<Protocol>](https://docs.rs/aws-smithy-http-server/latest/aws_smithy_http_server/request/trait.FromParts.html) with a `Rejection`
type that implements `std::fmt::Display` (preferably `std::error::Error`) to enable error logging when parameter construction from request parts fails.
See the [changelog discussion for futher details](https://github.com/smithy-lang/smithy-rs/discussions/3749).