Add hidden --preview / --no-preview options to ruff check (#7009)

Per discussion at https://github.com/astral-sh/ruff/discussions/6998

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Adds a `--preview` and `--no-preview` option to the CLI for `ruff check`
and corresponding settings. The CLI options are hidden for now.

Available in the settings as `preview = true` or `preview = false`.

Does not include environment variable configuration, although we may add
it in the future.

## Test Plan

<!-- How was it tested? -->

`cargo build`

Future work will build on this setting, such as toggling the mode during
a test.

crates/ruff_cli/src/args.rs

@@ -9,7 +9,7 @@ use rustc_hash::FxHashMap;
 use ruff::logging::LogLevel;
 use ruff::registry::Rule;
 use ruff::settings::types::{
-    FilePattern, PatternPrefixPair, PerFileIgnore, PythonVersion, SerializationFormat,
+    FilePattern, PatternPrefixPair, PerFileIgnore, PreviewMode, PythonVersion, SerializationFormat,
 };
 use ruff::RuleSelector;
 use ruff_workspace::configuration::{Configuration, RuleSelection};
@@ -115,6 +115,11 @@ pub struct CheckCommand {
     /// The minimum Python version that should be supported.
     #[arg(long, value_enum)]
     pub target_version: Option<PythonVersion>,
+    /// Enable preview mode; checks will include unstable rules and fixes.
+    #[arg(long, overrides_with("no_preview"), hide = true)]
+    preview: bool,
+    #[clap(long, overrides_with("preview"), hide = true)]
+    no_preview: bool,
     /// Path to the `pyproject.toml` or `ruff.toml` file to use for
     /// configuration.
     #[arg(long, conflicts_with = "isolated")]
@@ -458,6 +463,7 @@ impl CheckCommand {
                 ignore: self.ignore,
                 line_length: self.line_length,
                 per_file_ignores: self.per_file_ignores,
+                preview: resolve_bool_arg(self.preview, self.no_preview).map(PreviewMode::from),
                 respect_gitignore: resolve_bool_arg(
                     self.respect_gitignore,
                     self.no_respect_gitignore,
@@ -569,6 +575,7 @@ pub struct Overrides {
     pub ignore: Option<Vec<RuleSelector>>,
     pub line_length: Option<LineLength>,
     pub per_file_ignores: Option<Vec<PatternPrefixPair>>,
+    pub preview: Option<PreviewMode>,
     pub respect_gitignore: Option<bool>,
     pub select: Option<Vec<RuleSelector>>,
     pub show_source: Option<bool>,
@@ -632,6 +639,9 @@ impl ConfigProcessor for Overrides {
         if let Some(line_length) = &self.line_length {
             config.line_length = Some(*line_length);
         }
+        if let Some(preview) = &self.preview {
+            config.preview = Some(*preview);
+        }
         if let Some(per_file_ignores) = &self.per_file_ignores {
             config.per_file_ignores = Some(collect_per_file_ignores(per_file_ignores.clone()));
         }