Respect scoping rules when identifying builtins (#6468)

## Summary

Our `is_builtin` check did a naive walk over the parent scopes; instead,
it needs to (e.g.) skip symbols in a class scope if being called outside
of the class scope itself.

Closes #6466.

## Test Plan

`cargo test`

crates/ruff/resources/test/fixtures/pycodestyle/E721.py

@@ -61,3 +61,30 @@
 
 #: E721
 assert type(res) is int
+
+
+class Foo:
+    def asdf(self, value: str | None):
+        #: E721
+        if type(value) is str:
+            ...
+
+
+class Foo:
+    def type(self):
+        pass
+
+    def asdf(self, value: str | None):
+        #: E721
+        if type(value) is str:
+            ...
+
+
+class Foo:
+    def asdf(self, value: str | None):
+        def type():
+            pass
+
+        # Okay
+        if type(value) is str:
+            ...

crates/ruff/src/rules/pycodestyle/snapshots/ruff__rules__pycodestyle__tests__E721_E721.py.snap

@@ -152,4 +152,22 @@ E721.py:63:8: E721 Do not compare types, use `isinstance()`
    |        ^^^^^^^^^^^^^^^^ E721
    |
 
+E721.py:69:12: E721 Do not compare types, use `isinstance()`
+   |
+67 |     def asdf(self, value: str | None):
+68 |         #: E721
+69 |         if type(value) is str:
+   |            ^^^^^^^^^^^^^^^^^^ E721
+70 |             ...
+   |
+
+E721.py:79:12: E721 Do not compare types, use `isinstance()`
+   |
+77 |     def asdf(self, value: str | None):
+78 |         #: E721
+79 |         if type(value) is str:
+   |            ^^^^^^^^^^^^^^^^^^ E721
+80 |             ...
+   |
+
 

crates/ruff_python_semantic/src/model.rs

@@ -249,14 +249,16 @@ impl<'a> SemanticModel<'a> {
 
     /// Return `true` if `member` is bound as a builtin.
     pub fn is_builtin(&self, member: &str) -> bool {
-        self.find_binding(member)
+        self.lookup_symbol(member)
+            .map(|binding_id| &self.bindings[binding_id])
             .is_some_and(|binding| binding.kind.is_builtin())
     }
 
     /// Return `true` if `member` is an "available" symbol, i.e., a symbol that has not been bound
     /// in the current scope, or in any containing scope.
     pub fn is_available(&self, member: &str) -> bool {
-        self.find_binding(member)
+        self.lookup_symbol(member)
+            .map(|binding_id| &self.bindings[binding_id])
             .map_or(true, |binding| binding.kind.is_builtin())
     }