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-plugin-engine/src/context.rs

@@ -106,7 +106,7 @@ impl<'a> PluginExecutionContext for PluginExecutionCommandContext<'a> {
                 let span = value.span();
                 match value {
                     Value::Closure { val, .. } => {
-                        ClosureEvalOnce::new(&self.engine_state, &self.stack, val)
+                        ClosureEvalOnce::new(&self.engine_state, &self.stack, *val)
                             .run_with_input(PipelineData::Empty)
                             .map(|data| data.into_value(span))
                             .unwrap_or_else(|err| Value::error(err, self.call.head))