Minor: Derive Hash impls for CastOptions and FormatOptions (#4395)

Author: alamb

arrow-cast/src/cast.rs

@@ -57,7 +57,7 @@ use num::cast::AsPrimitive;
 use num::{NumCast, ToPrimitive};
 
 /// CastOptions provides a way to override the default cast behaviors
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct CastOptions<'a> {
     /// how to handle cast failures, either return NULL (safe=true) or return ERR (safe=false)
     pub safe: bool,

arrow-cast/src/display.rs

@@ -39,7 +39,7 @@ type TimeFormat<'a> = Option<&'a str>;
 /// By default nulls are formatted as `""` and temporal types formatted
 /// according to RFC3339
 ///
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct FormatOptions<'a> {
     /// If set to `true` any formatting errors will be written to the output
     /// instead of being converted into a [`std::fmt::Error`]