Boxes record for smaller Value enum. (#12252)

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# Description
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Boxes `Record` inside `Value` to reduce memory usage, `Value` goes from
`72` -> `56` bytes after this change.
# User-Facing Changes
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helps us keep track of breaking changes. -->

# Tests + Formatting
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crates/nu-command/src/formats/to/json.rs

@@ -135,7 +135,7 @@ pub fn value_to_json_value(v: &Value) -> Result<nu_json::Value, ShellError> {
         }
         Value::Record { val, .. } => {
             let mut m = nu_json::Map::new();
-            for (k, v) in val {
+            for (k, v) in &**val {
                 m.insert(k.clone(), value_to_json_value(v)?);
             }
             nu_json::Value::Object(m)

crates/nu-command/src/formats/to/nuon.rs

@@ -252,7 +252,7 @@ pub fn value_to_string(
         )),
         Value::Record { val, .. } => {
             let mut collection = vec![];
-            for (col, val) in val {
+            for (col, val) in &**val {
                 collection.push(if needs_quotes(col) {
                     format!(
                         "{idt_po}\"{}\": {}",

crates/nu-command/src/formats/to/toml.rs

@@ -60,7 +60,7 @@ fn helper(engine_state: &EngineState, v: &Value) -> Result<toml::Value, ShellErr
         Value::String { val, .. } | Value::Glob { val, .. } => toml::Value::String(val.clone()),
         Value::Record { val, .. } => {
             let mut m = toml::map::Map::new();
-            for (k, v) in val {
+            for (k, v) in &**val {
                 m.insert(k.clone(), helper(engine_state, v)?);
             }
             toml::Value::Table(m)

crates/nu-command/src/formats/to/xml.rs

@@ -331,7 +331,7 @@ impl Job {
             // content: null}, {tag: a}. See to_xml_entry for more
             let attrs = match attrs {
                 Value::Record { val, .. } => val,
-                Value::Nothing { .. } => Record::new(),
+                Value::Nothing { .. } => Box::new(Record::new()),
                 _ => {
                     return Err(ShellError::CantConvert {
                         to_type: "XML".into(),
@@ -355,7 +355,7 @@ impl Job {
                 }
             };
 
-            self.write_tag(entry_span, tag, tag_span, attrs, content)
+            self.write_tag(entry_span, tag, tag_span, *attrs, content)
         }
     }
 

crates/nu-command/src/formats/to/yaml.rs

@@ -57,7 +57,7 @@ pub fn value_to_yaml_value(v: &Value) -> Result<serde_yaml::Value, ShellError> {
         }
         Value::Record { val, .. } => {
             let mut m = serde_yaml::Mapping::new();
-            for (k, v) in val {
+            for (k, v) in &**val {
                 m.insert(
                     serde_yaml::Value::String(k.clone()),
                     value_to_yaml_value(v)?,