/// Trait for types that can sanitize their own fields.
///
/// Implement this on request/input structs to normalize data
/// (trim whitespace, lowercase emails, etc.) before validation.
///
/// The [`JsonRequest`](crate::extractor::JsonRequest),
/// [`FormRequest`](crate::extractor::FormRequest),
/// [`Query`](crate::extractor::Query), and
/// [`MultipartRequest`](crate::extractor::MultipartRequest) extractors call
/// [`Sanitize::sanitize`] automatically after deserialization, so every bound
/// on those extractors requires `T: Sanitize`.