add autofix for D301 (#7970)

## Summary

Add fix for `D301`

## Test Plan

`cargo test` and manually

crates/ruff_linter/resources/test/fixtures/pydocstyle/D301.py

@@ -10,6 +10,10 @@ def double_quotes_backslash_uppercase():
     R"""Sum\\mary."""
 
 
+def shouldnt_add_raw_here():
+    "Ruff \U000026a1"
+
+
 def make_unique_pod_id(pod_id: str) -> str | None:
     r"""
     Generate a unique Pod name.

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

@@ -1,6 +1,6 @@
 use memchr::memchr_iter;
 
-use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_text_size::Ranged;
 
@@ -46,18 +46,21 @@ use crate::docstrings::Docstring;
 #[violation]
 pub struct EscapeSequenceInDocstring;
 
-impl Violation for EscapeSequenceInDocstring {
+impl AlwaysFixableViolation for EscapeSequenceInDocstring {
     #[derive_message_formats]
     fn message(&self) -> String {
         format!(r#"Use `r"""` if any backslashes in a docstring"#)
     }
+
+    fn fix_title(&self) -> String {
+        format!(r#"Add `r` prefix"#)
+    }
 }
 
 /// D301
 pub(crate) fn backslashes(checker: &mut Checker, docstring: &Docstring) {
     // Docstring is already raw.
-    let contents = docstring.contents;
-    if contents.starts_with('r') || contents.starts_with("ur") {
+    if docstring.leading_quote().contains(['r', 'R']) {
         return;
     }
 
@@ -67,11 +70,15 @@ pub(crate) fn backslashes(checker: &mut Checker, docstring: &Docstring) {
     if memchr_iter(b'\\', bytes).any(|position| {
         let escaped_char = bytes.get(position.saturating_add(1));
         // Allow continuations (backslashes followed by newlines) and Unicode escapes.
-        !matches!(escaped_char, Some(b'\r' | b'\n' | b'u' | b'N'))
+        !matches!(escaped_char, Some(b'\r' | b'\n' | b'u' | b'U' | b'N'))
     }) {
-        checker.diagnostics.push(Diagnostic::new(
-            EscapeSequenceInDocstring,
+        let mut diagnostic = Diagnostic::new(EscapeSequenceInDocstring, docstring.range());
+
+        diagnostic.set_fix(Fix::unsafe_edit(Edit::range_replacement(
+            "r".to_owned() + docstring.contents,
             docstring.range(),
-        ));
+        )));
+
+        checker.diagnostics.push(diagnostic);
     }
 }

crates/ruff_linter/src/rules/pydocstyle/snapshots/ruff_linter__rules__pydocstyle__tests__D301_D.py.snap

@@ -1,28 +1,23 @@
 ---
 source: crates/ruff_linter/src/rules/pydocstyle/mod.rs
 ---
-D.py:328:5: D301 Use `r"""` if any backslashes in a docstring
-    |
-326 | @expect('D301: Use r""" if any backslashes in a docstring')
-327 | def single_quotes_raw_uppercase_backslash():
-328 |     R'Sum\mary.'
-    |     ^^^^^^^^^^^^ D301
-    |
-
-D.py:333:5: D301 Use `r"""` if any backslashes in a docstring
+D.py:333:5: D301 [*] Use `r"""` if any backslashes in a docstring
     |
 331 | @expect('D301: Use r""" if any backslashes in a docstring')
 332 | def double_quotes_backslash():
 333 |     """Sum\\mary."""
     |     ^^^^^^^^^^^^^^^^ D301
     |
+    = help: Add `r` prefix
 
-D.py:338:5: D301 Use `r"""` if any backslashes in a docstring
-    |
-336 | @expect('D301: Use r""" if any backslashes in a docstring')
-337 | def double_quotes_backslash_uppercase():
-338 |     R"""Sum\\mary."""
-    |     ^^^^^^^^^^^^^^^^^ D301
-    |
+ℹ Suggested fix
+330 330 | 
+331 331 | @expect('D301: Use r""" if any backslashes in a docstring')
+332 332 | def double_quotes_backslash():
+333     |-    """Sum\\mary."""
+    333 |+    r"""Sum\\mary."""
+334 334 | 
+335 335 | 
+336 336 | @expect('D301: Use r""" if any backslashes in a docstring')
 
 

crates/ruff_linter/src/rules/pydocstyle/snapshots/ruff_linter__rules__pydocstyle__tests__D301_D301.py.snap

@@ -1,18 +1,20 @@
 ---
 source: crates/ruff_linter/src/rules/pydocstyle/mod.rs
 ---
-D301.py:2:5: D301 Use `r"""` if any backslashes in a docstring
+D301.py:2:5: D301 [*] Use `r"""` if any backslashes in a docstring
   |
 1 | def double_quotes_backslash():
 2 |     """Sum\\mary."""
   |     ^^^^^^^^^^^^^^^^ D301
   |
+  = help: Add `r` prefix
 
-D301.py:10:5: D301 Use `r"""` if any backslashes in a docstring
-   |
- 9 | def double_quotes_backslash_uppercase():
-10 |     R"""Sum\\mary."""
-   |     ^^^^^^^^^^^^^^^^^ D301
-   |
+ℹ Suggested fix
+1 1 | def double_quotes_backslash():
+2   |-    """Sum\\mary."""
+  2 |+    r"""Sum\\mary."""
+3 3 | 
+4 4 | 
+5 5 | def double_quotes_backslash_raw():