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

tests/shell/pipeline/commands/internal.rs

@@ -29,7 +29,7 @@ fn takes_rows_of_nu_value_strings_and_pipes_it_to_stdin_of_external() {
 #[test]
 fn treats_dot_dot_as_path_not_range() {
     Playground::setup("dot_dot_dir", |dirs, sandbox| {
-        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+        sandbox.with_files(&[FileWithContentToBeTrimmed(
             "nu_times.csv",
             "
                 name,rusty_luck,origin
@@ -83,7 +83,7 @@ fn for_loop() {
 #[test]
 fn subexpression_handles_dot() {
     Playground::setup("subexpression_handles_dot", |dirs, sandbox| {
-        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+        sandbox.with_files(&[FileWithContentToBeTrimmed(
             "nu_times.csv",
             "
                 name,rusty_luck,origin