feat: impl<B> for (From/Into)Value for Cow<'_, B> where B::Owned: (From/Into)Value (#16380)

# Description
Implements `FromValue` and `IntoValue` for `Cow`, which makes it easy to
use it in types that need to implement these traits.

I don't think it will have a significant impact, but it can let us avoid
allocations where we can use static values.

# Tests + Formatting
No need, the implementations are delegated to `B::Owned`.

Co-authored-by: Bahex <Bahex@users.noreply.github.com>

crates/nu-protocol/src/value/from_value.rs

@@ -7,6 +7,7 @@ use crate::{
 use chrono::{DateTime, FixedOffset};
 use std::{
     any,
+    borrow::Cow,
     cmp::Ordering,
     collections::{HashMap, VecDeque},
     fmt,
@@ -564,6 +565,25 @@ where
     }
 }
 
+/// This blanket implementation permits the use of [`Cow<'_, B>`] ([`Cow<'_, str>`] etc) based on
+/// the [FromValue] implementation of `B`'s owned form ([str] => [String]).
+///
+/// It's meant to make using the [FromValue] derive macro on types that contain [Cow] fields
+/// possible.
+impl<B> FromValue for Cow<'_, B>
+where
+    B: ?Sized + ToOwned,
+    B::Owned: FromValue,
+{
+    fn from_value(v: Value) -> Result<Self, ShellError> {
+        <B::Owned as FromValue>::from_value(v).map(Cow::Owned)
+    }
+
+    fn expected_type() -> Type {
+        <B::Owned as FromValue>::expected_type()
+    }
+}
+
 impl<V> FromValue for HashMap<String, V>
 where
     V: FromValue,

crates/nu-protocol/src/value/into_value.rs

@@ -1,6 +1,9 @@
 use crate::{Range, Record, ShellError, Span, Value, ast::CellPath, engine::Closure};
 use chrono::{DateTime, FixedOffset};
-use std::{borrow::Borrow, collections::HashMap};
+use std::{
+    borrow::{Borrow, Cow},
+    collections::HashMap,
+};
 
 /// A trait for converting a value into a [`Value`].
 ///
@@ -202,6 +205,21 @@ where
     }
 }
 
+/// This blanket implementation permits the use of [`Cow<'_, B>`] ([`Cow<'_, str>`] etc) based on
+/// the [IntoValue] implementation of `B`'s owned form ([str] => [String]).
+///
+/// It's meant to make using the [IntoValue] derive macro on types that contain [Cow] fields
+/// possible.
+impl<B> IntoValue for Cow<'_, B>
+where
+    B: ?Sized + ToOwned,
+    B::Owned: IntoValue,
+{
+    fn into_value(self, span: Span) -> Value {
+        <B::Owned as IntoValue>::into_value(self.into_owned(), span)
+    }
+}
+
 impl<K, V> IntoValue for HashMap<K, V>
 where
     K: Borrow<str> + Into<String>,