Revert "Remove --line-length option from format command (#8131)"

This reverts commit 2f32a57.

crates/ruff_cli/src/args.rs

@@ -409,6 +409,9 @@ pub struct FormatCommand {
     force_exclude: bool,
     #[clap(long, overrides_with("force_exclude"), hide = true)]
     no_force_exclude: bool,
+    /// Set the line-length.
+    #[arg(long, help_heading = "Rule configuration", hide = true)]
+    pub line_length: Option<LineLength>,
     /// Ignore all configuration files.
     #[arg(long, conflicts_with = "config", help_heading = "Miscellaneous")]
     pub isolated: bool,
@@ -552,6 +555,7 @@ impl FormatCommand {
                 stdin_filename: self.stdin_filename,
             },
             CliOverrides {
+                line_length: self.line_length,
                 respect_gitignore: resolve_bool_arg(
                     self.respect_gitignore,
                     self.no_respect_gitignore,

crates/ruff_python_formatter/README.md

@@ -117,10 +117,11 @@ quote-style = "single"
 ```
 
 The Ruff formatter also respects Ruff's [`line-length`](https://docs.astral.sh/ruff/settings/#line-length)
-setting, which also can be provided via a `pyproject.toml` or `ruff.toml` file.
+setting, which also can be provided via a `pyproject.toml` or `ruff.toml` file, or on the CLI, as
+in:
 
-```toml
-line-length = 80
+```console
+ruff format --line-length 100 /path/to/file.py
 ```
 
 ### Excluding code from formatting