Use variable names directly in the format strings (#7906)

# Description

Lint: `clippy::uninlined_format_args`

More readable in most situations.
(May be slightly confusing for modifier format strings
https://doc.rust-lang.org/std/fmt/index.html#formatting-parameters)

Alternative to #7865

# User-Facing Changes

None intended

# Tests + Formatting

(Ran `cargo +stable clippy --fix --workspace -- -A clippy::all -D
clippy::uninlined_format_args` to achieve this. Depends on Rust `1.67`)

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

@@ -33,7 +33,7 @@ pub fn ensure_binary_present(package: &str) {
             .read_to_string(&mut buffer)
             .expect("failed to read cargo build stderr");
         if !buffer.is_empty() {
-            println!("=== cargo build stderr\n{}", buffer);
+            println!("=== cargo build stderr\n{buffer}");
         }
     }
 

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

@@ -95,7 +95,7 @@ impl Executable for Director {
                         if !commands.is_empty() {
                             commands.push_str("| ");
                         }
-                        let _ = writeln!(commands, "{}", pipeline);
+                        let _ = writeln!(commands, "{pipeline}");
                     }
                 }
 
@@ -104,7 +104,7 @@ impl Executable for Director {
                     .stdout(Stdio::piped())
                     // .stdin(Stdio::piped())
                     .stderr(Stdio::piped())
-                    .arg(format!("-c '{}'", commands))
+                    .arg(format!("-c '{commands}'"))
                     .spawn()
                     .expect("It should be possible to run tests");
 

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

@@ -49,12 +49,11 @@ impl CheckerMatchers for Play {
             None => return Ok(()),
         };
         let actual =
-            str::from_utf8(actual).map_err(|_| format!("{} was not utf8 encoded", description))?;
+            str::from_utf8(actual).map_err(|_| format!("{description} was not utf8 encoded"))?;
 
         if actual != *out {
             return Err(format!(
-                "not equal:\n    actual: {}\n  expected: {}\n\n",
-                actual, out
+                "not equal:\n    actual: {actual}\n  expected: {out}\n\n"
             ));
         }
 
@@ -77,7 +76,7 @@ impl Matcher<Director> for Play {
 impl<'a> Matcher<&'a mut Director> for Play {
     fn matches(&self, director: &'a mut Director) -> MatchResult {
         if director.executable().is_none() {
-            return Err(format!("no such process {}", director));
+            return Err(format!("no such process {director}"));
         }
 
         let res = director.execute();
@@ -89,7 +88,7 @@ impl<'a> Matcher<&'a mut Director> for Play {
                     return self.output(out);
                 }
 
-                Err(format!("could not exec process {}: {:?}", director, err))
+                Err(format!("could not exec process {director}: {err:?}"))
             }
         }
     }