Avoid fixing D200 for docstrings that end in escapes (#6779)

Appease the fuzzers! Closes
https://github.com/astral-sh/ruff/issues/6755.

crates/ruff/resources/test/fixtures/pydocstyle/D200.py

@@ -0,0 +1,13 @@
+def func():
+    """\
+    """
+
+
+def func():
+    """\\
+    """
+
+
+def func():
+    """\ \
+    """

crates/ruff/src/rules/pydocstyle/mod.rs

@@ -39,6 +39,7 @@ mod tests {
     #[test_case(Rule::NewLineAfterLastParagraph, Path::new("D.py"))]
     #[test_case(Rule::NewLineAfterSectionName, Path::new("sections.py"))]
     #[test_case(Rule::NoBlankLineAfterFunction, Path::new("D.py"))]
+    #[test_case(Rule::FitsOnOneLine, Path::new("D200.py"))]
     #[test_case(Rule::NoBlankLineAfterFunction, Path::new("D202.py"))]
     #[test_case(Rule::BlankLineBeforeClass, Path::new("D.py"))]
     #[test_case(Rule::NoBlankLineBeforeFunction, Path::new("D.py"))]

crates/ruff/src/rules/pydocstyle/rules/one_liner.rs

@@ -74,7 +74,8 @@ pub(crate) fn one_liner(checker: &mut Checker, docstring: &Docstring) {
                 // characters, avoid applying the fix.
                 let body = docstring.body();
                 let trimmed = body.trim();
-                if !trimmed.ends_with(trailing.chars().last().unwrap())
+                if trimmed.chars().rev().take_while(|c| *c == '\\').count() % 2 == 0
+                    && !trimmed.ends_with(trailing.chars().last().unwrap())
                     && !trimmed.starts_with(leading.chars().last().unwrap())
                 {
                     diagnostic.set_fix(Fix::suggested(Edit::range_replacement(

crates/ruff/src/rules/pydocstyle/snapshots/ruff__rules__pydocstyle__tests__D200_D200.py.snap

@@ -0,0 +1,45 @@
+---
+source: crates/ruff/src/rules/pydocstyle/mod.rs
+---
+D200.py:2:5: D200 One-line docstring should fit on one line
+  |
+1 |   def func():
+2 |       """\
+  |  _____^
+3 | |     """
+  | |_______^ D200
+  |
+  = help: Reformat to one line
+
+D200.py:7:5: D200 [*] One-line docstring should fit on one line
+  |
+6 |   def func():
+7 |       """\\
+  |  _____^
+8 | |     """
+  | |_______^ D200
+  |
+  = help: Reformat to one line
+
+ℹ Suggested fix
+4 4 | 
+5 5 | 
+6 6 | def func():
+7   |-    """\\
+8   |-    """
+  7 |+    """\\"""
+9 8 | 
+10 9 | 
+11 10 | def func():
+
+D200.py:12:5: D200 One-line docstring should fit on one line
+   |
+11 |   def func():
+12 |       """\ \
+   |  _____^
+13 | |     """
+   | |_______^ D200
+   |
+   = help: Reformat to one line
+
+