Shrink Value by boxing Range/Closure (#12784)

# Description
On 64-bit platforms the current size of `Value` is 56 bytes. The
limiting variants were `Closure` and `Range`. Boxing the two reduces the
size of Value to 48 bytes. This is the minimal size possible with our
current 16-byte `Span` and any 24-byte `Vec` container which we use in
several variants. (Note the extra full 8-bytes necessary for the
discriminant or other smaller values due to the 8-byte alignment of
`usize`)

This is leads to a size reduction of ~15% for `Value` and should overall
be beneficial as both `Range` and `Closure` are rarely used compared to
the primitive types or even our general container types.

# User-Facing Changes
Less memory used, potential runtime benefits.

(Too late in the evening to run the benchmarks myself right now)

crates/nu-color-config/src/style_computer.rs

@@ -146,7 +146,10 @@ impl<'a> StyleComputer<'a> {
             let span = value.span();
             match value {
                 Value::Closure { val, .. } => {
-                    map.insert(key.to_string(), ComputableStyle::Closure(val.clone(), span));
+                    map.insert(
+                        key.to_string(),
+                        ComputableStyle::Closure(*val.clone(), span),
+                    );
                 }
                 Value::Record { .. } => {
                     map.insert(