--show-settings displays active settings in a far more readable format (#9464)

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## Summary

Fixes #8334.

`Display` has been implemented for `ruff_workspace::Settings`, which
gives a much nicer and more readable output to `--show-settings`.

Internally, a `display_settings` utility macro has been implemented to
reduce the boilerplate of the display code.

### Work to be done

- [x] A lot of formatting for `Vec<_>` and `HashSet<_>` types have been
stubbed out, using `Debug` as a fallback. There should be a way to add
generic formatting support for these types as a modifier in
`display_settings`.
- [x] Several complex types were also stubbed out and need proper
`Display` implementations rather than falling back on `Debug`.
- [x] An open question needs to be answered: how important is it that
the output be valid TOML? Some types in settings, such as a hash-map
from a glob pattern to a multi-variant enum, will be hard to rework into
valid _and_ readable TOML.
- [x] Tests need to be implemented.

## Test Plan

Tests consist of a snapshot test for the default `--show-settings`
output and a doctest for `display_settings!`.

crates/ruff_linter/src/rules/pydocstyle/settings.rs

@@ -1,9 +1,11 @@
 //! Settings for the `pydocstyle` plugin.
 
 use std::collections::BTreeSet;
+use std::fmt;
 
 use serde::{Deserialize, Serialize};
 
+use crate::display_settings;
 use ruff_macros::CacheKey;
 
 use crate::registry::Rule;
@@ -71,9 +73,34 @@ impl Convention {
     }
 }
 
+impl fmt::Display for Convention {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Google => write!(f, "google"),
+            Self::Numpy => write!(f, "numpy"),
+            Self::Pep257 => write!(f, "pep257"),
+        }
+    }
+}
+
 #[derive(Debug, Default, CacheKey)]
 pub struct Settings {
     pub convention: Option<Convention>,
     pub ignore_decorators: BTreeSet<String>,
     pub property_decorators: BTreeSet<String>,
 }
+
+impl fmt::Display for Settings {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        display_settings! {
+            formatter = f,
+            namespace = "linter.pydocstyle",
+            fields = [
+                self.convention | optional,
+                self.ignore_decorators | debug,
+                self.property_decorators | debug
+            ]
+        }
+        Ok(())
+    }
+}