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/table.rs

@@ -505,7 +505,7 @@ fn external_with_too_much_stdout_should_not_hang_nu() {
         for _ in 0..bytes {
             large_file_body.push('a');
         }
-        sandbox.with_files(vec![FileWithContent("a_large_file.txt", &large_file_body)]);
+        sandbox.with_files(&[FileWithContent("a_large_file.txt", &large_file_body)]);
 
         let actual = nu!(
             cwd: dirs.test(), pipeline(
@@ -536,7 +536,7 @@ fn table_index_0() {
 #[test]
 fn test_expand_big_0() {
     Playground::setup("test_expand_big_0", |dirs, sandbox| {
-        sandbox.with_files(vec![FileWithContent(
+        sandbox.with_files(&[FileWithContent(
             "sample.toml",
             r#"
             [package]
@@ -1820,7 +1820,7 @@ fn table_expande_with_no_header_internally_1() {
 #[test]
 fn test_collapse_big_0() {
     Playground::setup("test_expand_big_0", |dirs, sandbox| {
-        sandbox.with_files(vec![FileWithContent(
+        sandbox.with_files(&[FileWithContent(
             "sample.toml",
             r#"
             [package]