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/last.rs

@@ -15,7 +15,7 @@ fn gets_the_last_row() {
 #[test]
 fn gets_last_rows_by_amount() {
     Playground::setup("last_test_1", |dirs, sandbox| {
-        sandbox.with_files(vec![
+        sandbox.with_files(&[
             EmptyFile("los.txt"),
             EmptyFile("tres.txt"),
             EmptyFile("amigos.txt"),
@@ -31,7 +31,7 @@ fn gets_last_rows_by_amount() {
 #[test]
 fn gets_last_row_when_no_amount_given() {
     Playground::setup("last_test_2", |dirs, sandbox| {
-        sandbox.with_files(vec![EmptyFile("caballeros.txt"), EmptyFile("arepas.clu")]);
+        sandbox.with_files(&[EmptyFile("caballeros.txt"), EmptyFile("arepas.clu")]);
 
         // FIXME: We should probably change last to return a one row table instead of a record here
         let actual = nu!(cwd: dirs.test(), "ls | last | values | length");