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-plugin/src/protocol/mod.rs

@@ -60,13 +60,13 @@ impl From<ShellError> for LabeledError {
                 LabeledError { label, msg, span }
             }
             ShellError::CantConvert(expected, input, span, _help) => LabeledError {
-                label: format!("Can't convert to {}", expected),
-                msg: format!("can't convert {} to {}", expected, input),
+                label: format!("Can't convert to {expected}"),
+                msg: format!("can't convert {expected} to {input}"),
                 span: Some(span),
             },
             ShellError::DidYouMean(suggestion, span) => LabeledError {
                 label: "Name not found".into(),
-                msg: format!("did you mean '{}'", suggestion),
+                msg: format!("did you mean '{suggestion}'"),
                 span: Some(span),
             },
             ShellError::PluginFailedToLoad(msg) => LabeledError {

crates/nu-plugin/src/protocol/plugin_custom_value.rs

@@ -56,7 +56,7 @@ impl CustomValue for PluginCustomValue {
                     "Unable to spawn plugin for {} to get base value",
                     self.source
                 ),
-                format!("{}", err),
+                format!("{err}"),
                 Some(span),
                 None,
                 Vec::new(),
@@ -85,7 +85,7 @@ impl CustomValue for PluginCustomValue {
                     "Unable to decode call for {} to get base value",
                     self.source
                 ),
-                format!("{}", err),
+                format!("{err}"),
                 Some(span),
                 None,
                 Vec::new(),