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-command/src/strings/str_/trim/trim_.rs

@@ -266,10 +266,10 @@ fn trim(s: &str, char_: Option<char>, closure_flags: &ClosureFlags) -> String {
                 '\x0B' => r"\v".to_string(),
                 '\x0C' => r"\f".to_string(),
                 '\x0D' => r"\r".to_string(),
-                _ => format!(r"\{}", r),
+                _ => format!(r"\{r}"),
             };
             // create a regex string that looks for 2 or more of each of these characters
-            let re_str = format!("{}{{2,}}", reg);
+            let re_str = format!("{reg}{{2,}}");
             // create the regex
             let re = Regex::new(&re_str).expect("Error creating regular expression");
             // replace all multiple occurrences with single occurrences represented by r