Deref &String arguments to &str where appropriate (#10321)

# Description
This generally makes for nicer APIs, as you are not forced to use an
existing allocation covering the full `String`.

Some exceptions remain where the underlying type requirements favor it.

# User-Facing Changes
None

crates/nu-test-support/src/macros.rs

@@ -469,9 +469,9 @@ pub fn read_std(std: &[u8]) -> String {
     out.replace('\n', "")
 }
 
-use std::{path::PathBuf, process::Command};
+use std::{path::Path, process::Command};
 
-pub fn run_command(executable_path: &PathBuf, target_cwd: &str) -> Command {
+pub fn run_command(executable_path: &Path, target_cwd: &str) -> Command {
     let mut command = Command::new(executable_path);
 
     command

crates/nu-test-support/src/playground/matchers.rs

@@ -30,7 +30,7 @@ pub fn says() -> Play {
 
 trait CheckerMatchers {
     fn output(&self, actual: &Outcome) -> MatchResult;
-    fn std(&self, actual: &[u8], expected: Option<&String>, description: &str) -> MatchResult;
+    fn std(&self, actual: &[u8], expected: Option<&str>, description: &str) -> MatchResult;
     fn stdout(&self, actual: &Outcome) -> MatchResult;
 }
 
@@ -40,10 +40,10 @@ impl CheckerMatchers for Play {
     }
 
     fn stdout(&self, actual: &Outcome) -> MatchResult {
-        self.std(&actual.out, self.stdout_expectation.as_ref(), "stdout")
+        self.std(&actual.out, self.stdout_expectation.as_deref(), "stdout")
     }
 
-    fn std(&self, actual: &[u8], expected: Option<&String>, description: &str) -> MatchResult {
+    fn std(&self, actual: &[u8], expected: Option<&str>, description: &str) -> MatchResult {
         let out = match expected {
             Some(out) => out,
             None => return Ok(()),
@@ -51,7 +51,7 @@ impl CheckerMatchers for Play {
         let actual =
             str::from_utf8(actual).map_err(|_| format!("{description} was not utf8 encoded"))?;
 
-        if actual != *out {
+        if actual != out {
             return Err(format!(
                 "not equal:\n    actual: {actual}\n  expected: {out}\n\n"
             ));

crates/nu-test-support/src/playground/play.rs

@@ -46,12 +46,12 @@ impl Dirs {
         self.fixtures.join("playground/config")
     }
 
-    pub fn root(&self) -> &PathBuf {
-        &self.root
+    pub fn root(&self) -> &Path {
+        self.root.as_path()
     }
 
-    pub fn test(&self) -> &PathBuf {
-        &self.test
+    pub fn test(&self) -> &Path {
+        self.test.as_path()
     }
 }