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/src/conversions/into/datetime.rs

@@ -39,7 +39,7 @@ impl Zone {
             Self::Error // Out of range
         }
     }
-    fn from_string(s: String) -> Self {
+    fn from_string(s: &str) -> Self {
         match s.to_ascii_lowercase().as_str() {
             "utc" | "u" => Self::Utc,
             "local" | "l" => Self::Local,
@@ -126,7 +126,7 @@ impl Command for SubCommand {
                         span: zone_offset.span,
                     }),
                     None => timezone.as_ref().map(|zone| Spanned {
-                        item: Zone::from_string(zone.item.clone()),
+                        item: Zone::from_string(&zone.item),
                         span: zone.span,
                     }),
                 };