Avoid taking unnecessary ownership of intermediates (#12740)

# Description

Judiciously try to avoid allocations/clone by changing the signature of
functions

- **Don't pass str by value unnecessarily if only read**
- **Don't require a vec in `Sandbox::with_files`**
- **Remove unnecessary string clone**
- **Fixup unnecessary borrow**
- **Use `&str` in shape color instead**
- **Vec -> Slice**
- **Elide string clone**
- **Elide `Path` clone**
- **Take &str to elide clone in tests**

# User-Facing Changes
None

# Tests + Formatting
This touches many tests purely in changing from owned to borrowed/static
data

crates/nu-cli/src/syntax_highlight.rs

@@ -88,7 +88,7 @@ impl Highlighter for NuHighlighter {
                 .to_string();
 
             let mut add_colored_token = |shape: &FlatShape, text: String| {
-                output.push((get_shape_color(shape.to_string(), &self.config), text));
+                output.push((get_shape_color(shape.as_str(), &self.config), text));
             };
 
             match shape.1 {
@@ -128,7 +128,7 @@ impl Highlighter for NuHighlighter {
                         let start = part.start - span.start;
                         let end = part.end - span.start;
                         let text = next_token[start..end].to_string();
-                        let mut style = get_shape_color(shape.to_string(), &self.config);
+                        let mut style = get_shape_color(shape.as_str(), &self.config);
                         if highlight {
                             style = get_matching_brackets_style(style, &self.config);
                         }