numfmt: simplify write_line buffering logic

Flatten the nested block scope by moving the output trait object and
format dispatch to the same level, reducing indentation.

Author: sylvestre

src/uu/numfmt/src/numfmt.rs

@@ -96,25 +96,19 @@ fn write_line<W: std::io::Write>(
         None => input_line,
     };
     let buffer_output = !matches!(options.invalid, InvalidModes::Abort);
-    let mut formatted_line = Vec::new();
-    let handled_line = {
-        let output: &mut dyn std::io::Write = if buffer_output {
-            &mut formatted_line
-        } else {
-            writer
-        };
+    let mut buf = Vec::new();
+    let output: &mut dyn std::io::Write = if buffer_output { &mut buf } else { writer };
 
-        if options.delimiter.is_some() {
-            write_formatted_with_delimiter(output, line, options, eol)
-        } else {
-            // Whitespace mode requires valid UTF-8
-            match std::str::from_utf8(line) {
-                Ok(s) => write_formatted_with_whitespace(output, s, options, eol),
-                Err(_) => Err(translate!(
-                    "numfmt-error-invalid-number",
-                    "input" => escape_line(line).quote()
-                )),
-            }
+    let handled_line = if options.delimiter.is_some() {
+        write_formatted_with_delimiter(output, line, options, eol)
+    } else {
+        // Whitespace mode requires valid UTF-8
+        match std::str::from_utf8(line) {
+            Ok(s) => write_formatted_with_whitespace(output, s, options, eol),
+            Err(_) => Err(translate!(
+                "numfmt-error-invalid-number",
+                "input" => escape_line(line).quote()
+            )),
         }
     };
 
@@ -132,15 +126,14 @@ fn write_line<W: std::io::Write>(
             InvalidModes::Ignore => {}
         }
         writer.write_all(input_line)?;
-
         if let Some(eol) = eol {
             writer.write_all(&[eol])?;
         }
         return Ok(true);
     }
 
     if buffer_output {
-        writer.write_all(&formatted_line)?;
+        writer.write_all(&buf)?;
     }
     Ok(false)
 }