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-parser/tests/test_parser.rs

@@ -1595,8 +1595,8 @@ mod input_types {
         for input in inputs {
             let (block, err) = parse(&mut working_set, None, input.as_bytes(), true, &[]);
 
-            assert!(err.is_none(), "testing: {}", input);
-            assert_eq!(block.len(), 2, "testing: {}", input);
+            assert!(err.is_none(), "testing: {input}");
+            assert_eq!(block.len(), 2, "testing: {input}");
         }
     }
 

crates/nu-parser/tests/test_parser_unicode_escapes.rs

@@ -29,15 +29,13 @@ pub fn do_test(test: &[u8], expected: &str, error_contains: Option<&str>) {
         }
         Some(pev) => match error_contains {
             None => {
-                panic!("Err:{:#?}", pev);
+                panic!("Err:{pev:#?}");
             }
             Some(contains_string) => {
-                let full_err = format!("{:#?}", pev);
+                let full_err = format!("{pev:#?}");
                 assert!(
                     full_err.contains(contains_string),
-                    "Expected error containing {}, instead got {}",
-                    contains_string,
-                    full_err
+                    "Expected error containing {contains_string}, instead got {full_err}"
                 );
             }
         },