[`pycodestyle`] Fix `E301` to only trigger for functions immediately within a class (#19768)

## Summary

Fixes #19752

---------

Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>

crates/ruff_linter/resources/test/fixtures/pycodestyle/E30.py

@@ -974,3 +974,39 @@ BANANA = 100
 APPLE = 200
 
 # end
+
+
+# https://github.com/astral-sh/ruff/issues/19752
+class foo:
+    async def recv(self, *, length=65536):
+        loop = asyncio.get_event_loop()
+        def callback():
+            loop.remove_reader(self._fd)
+        loop.add_reader(self._fd, callback)
+# end
+
+
+# E301
+class Foo:
+    if True:
+        print("conditional")
+        def test():
+            pass
+# end
+
+
+# Test case for nested class scenario
+class Bar:
+    def f():
+        x = 1
+        def g():
+            return 1
+        return 2
+
+    def f():
+        class Baz:
+            x = 1
+            def g():
+                return 1
+            return 2
+# end

crates/ruff_linter/src/rules/pycodestyle/rules/blank_lines.rs

@@ -836,7 +836,10 @@ impl<'a, 'b> BlankLinesChecker<'a, 'b> {
             // Allow groups of one-liners.
             && !(state.follows.is_any_def() && line.last_token != TokenKind::Colon)
             && !state.follows.follows_def_with_dummy_body()
+            // Only for class scope: we must be inside a class block
             && matches!(state.class_status, Status::Inside(_))
+            // But NOT inside a function body; nested defs inside methods are handled by E306
+            && matches!(state.fn_status, Status::Outside | Status::CommentAfter(_))
             // The class/parent method's docstring can directly precede the def.
             // Allow following a decorator (if there is an error it will be triggered on the first decorator).
             && !matches!(state.follows, Follows::Docstring | Follows::Decorator)

crates/ruff_linter/src/rules/pycodestyle/snapshots/ruff_linter__rules__pycodestyle__tests__E301_E30.py.snap

@@ -94,3 +94,22 @@ help: Add missing blank line
 527 |     def bar(self, x: int | str) -> int | str:
 528 |         return x
 529 | # end
+
+E301 [*] Expected 1 blank line, found 0
+   --> E30.py:993:9
+    |
+991 |     if True:
+992 |         print("conditional")
+993 |         def test():
+    |         ^^^
+994 |             pass
+995 | # end
+    |
+help: Add missing blank line
+990 | class Foo:
+991 |     if True:
+992 |         print("conditional")
+993 + 
+994 |         def test():
+995 |             pass
+996 | # end

crates/ruff_linter/src/rules/pycodestyle/snapshots/ruff_linter__rules__pycodestyle__tests__E306_E30.py.snap

@@ -208,3 +208,60 @@ help: Add missing blank line
 926 |     async def b():
 927 |         pass
 928 | # end
+
+E306 [*] Expected 1 blank line before a nested definition, found 0
+   --> E30.py:983:9
+    |
+981 |     async def recv(self, *, length=65536):
+982 |         loop = asyncio.get_event_loop()
+983 |         def callback():
+    |         ^^^
+984 |             loop.remove_reader(self._fd)
+985 |         loop.add_reader(self._fd, callback)
+    |
+help: Add missing blank line
+980 | class foo:
+981 |     async def recv(self, *, length=65536):
+982 |         loop = asyncio.get_event_loop()
+983 + 
+984 |         def callback():
+985 |             loop.remove_reader(self._fd)
+986 |         loop.add_reader(self._fd, callback)
+
+E306 [*] Expected 1 blank line before a nested definition, found 0
+    --> E30.py:1002:9
+     |
+1000 |     def f():
+1001 |         x = 1
+1002 |         def g():
+     |         ^^^
+1003 |             return 1
+1004 |         return 2
+     |
+help: Add missing blank line
+999  | class Bar:
+1000 |     def f():
+1001 |         x = 1
+1002 + 
+1003 |         def g():
+1004 |             return 1
+1005 |         return 2
+
+E306 [*] Expected 1 blank line before a nested definition, found 0
+    --> E30.py:1009:13
+     |
+1007 |         class Baz:
+1008 |             x = 1
+1009 |             def g():
+     |             ^^^
+1010 |                 return 1
+1011 |             return 2
+     |
+help: Add missing blank line
+1006 |     def f():
+1007 |         class Baz:
+1008 |             x = 1
+1009 + 
+1010 |             def g():
+1011 |                 return 1
+1012 |             return 2