Saved cookiejars with partitioned cookies are unable to be loaded in python <= 3.13

[Cycloctane]

Describe the bug

aiohttp use __setitem__ to make cookie's partitioned attribute available in python <= 3.13 (#11112 ):

aiohttp/aiohttp/_cookie_helpers.py

Lines 274 to 275 in 230e1ee

	if lower_key == "partitioned" and sys.version_info < (3, 14):
	dict.__setitem__(current_morsel, lower_key, True)

This actually makes pickled cookies contain attribute not supported in standard http.cookie. Pickled cookiejars are not able to be unpickled if they contain partitioned cookies.

To Reproduce

from aiohttp import CookieJar

cj = CookieJar()
cj.update_cookies_from_headers(["a=a; Partitioned"], response_url=URL("http://example.com/"))
cj.save("cookies.bin")
CookieJar().load("cookies.bin")

File "D:\Program Files\Python311\Lib\site-packages\aiohttp\cookiejar.py", line 133, in load
    self._cookies = pickle.load(f)
                    ^^^^^^^^^^^^^^
  File "D:\Program Files\Python311\Lib\http\cookies.py", line 312, in __setitem__
    raise CookieError("Invalid attribute %r" % (K,))
http.cookies.CookieError: Invalid attribute 'partitioned'

Python Version

<=3.13

aiohttp Version

>=3.12.7

[Dreamsorcerer]

Yeah, that code is unfortunately complex. We should be able to revert it in Python 3.15+ (python/cpython#113663), but until then I guess we just need to deal with the hacks.

I guess partitioned cookies should mostly be unused in Python <3.14 and we can maybe just ignore this issue. Unless someone has an easy fix..

[Cycloctane]

I guess partitioned cookies should mostly be unused in Python <3.14 and we can maybe just ignore this issue. Unless someone has an easy fix..

                 if lower_key in _COOKIE_BOOL_ATTRS:
                     # Boolean attribute with any value should be True
-                    if current_morsel is not None:
-                        if lower_key == "partitioned" and sys.version_info < (3, 14):
-                            dict.__setitem__(current_morsel, lower_key, True)
-                        else:
-                            current_morsel[lower_key] = True
+                    if current_morsel is not None and current_morsel.isReservedKey(lower_key):
+                        current_morsel[lower_key] = True
                 elif value is None:
                     # Invalid cookie string - non-boolean attribute without value
                     break

Does it make sense to let partitioned flag only available if http.cookies supports it (python >= 3.14 or monkey-patched by users)? If users are not aware of partitioned cookies feature, ignore this flag without breaking cookie parsing to avoid problems caused by custom attributes.

[bdraco]

I think the patch you are proposing makes sense. There isn't much use for partitioned unless its been monkey patched or 3.14+