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/src/parse_keywords.rs

@@ -3561,7 +3561,7 @@ pub fn parse_register(
                     Ok(path)
                 } else {
                     Err(ParseError::RegisteredFileNotFound(
-                        format!("{:?}", path),
+                        format!("{path:?}"),
                         expr.span,
                     ))
                 }
@@ -3576,7 +3576,7 @@ pub fn parse_register(
         serde_json::from_slice::<Signature>(signature).map_err(|e| {
             ParseError::LabeledError(
                 "Signature deserialization error".into(),
-                format!("unable to deserialize signature: {}", e),
+                format!("unable to deserialize signature: {e}"),
                 spans[0],
             )
         })
@@ -3597,7 +3597,7 @@ pub fn parse_register(
                     Ok(path)
                 } else {
                     Err(ParseError::RegisteredFileNotFound(
-                        format!("{:?}", path),
+                        format!("{path:?}"),
                         expr.span,
                     ))
                 }