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-command/tests/commands/du.rs

@@ -51,7 +51,7 @@ fn test_du_flag_max_depth() {
 #[case("a][c")]
 fn du_files_with_glob_metachars(#[case] src_name: &str) {
     Playground::setup("du_test_16", |dirs, sandbox| {
-        sandbox.with_files(vec![EmptyFile(src_name)]);
+        sandbox.with_files(&[EmptyFile(src_name)]);
 
         let src = dirs.test().join(src_name);