Bundle misc/proper_plugin.py as a part of mypy

[sobolevn]

I modified

diff --git mypy/binder.py mypy/binder.py
index 8a68f24f6..194883f86 100644
--- mypy/binder.py
+++ mypy/binder.py
@@ -345,7 +345,7 @@ class ConditionalTypeBinder:
             self._cleanse_key(dep)
 
     def most_recent_enclosing_type(self, expr: BindableExpression, type: Type) -> Type | None:
-        type = get_proper_type(type)
+        # type = get_proper_type(type)
         if isinstance(type, AnyType):
             return get_declaration(expr)
         key = literal_hash(expr)

to see if it still works. It is:

» python runtests.py self
run self: ['/Users/sobolev/Desktop/mypy/.venv/bin/python', '-m', 'mypy', '--config-file', 'mypy_self_check.ini', '-p', 'mypy', '-p', 'mypyc']
mypy/binder.py:349: error: Never apply isinstance() to unexpanded types; use
mypy.types.get_proper_type() first  [misc]
            if isinstance(type, AnyType):
               ^~~~~~~~~~~~~~~~~~~~~~~~~
mypy/binder.py:349: note: If you pass on the original type after the check, always use its unexpanded version
Found 1 error in 1 file (checked 288 source files)

FAILED: self

I will add this plugin to my CI checks in like ~5 plugins I maintain :)

• https://github.com/typeddjango/django-stubs
• https://github.com/typeddjango/djangorestframework-stubs
• https://github.com/dry-python/returns
• https://github.com/dry-python/classes
• https://github.com/wemake-services/mypy-extras

Closes #16035

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[sobolevn]

Thanks! 👍