feat: add cookies and host_only_cookies properties to CookieJar

[Br1an67]

What do these changes do?

Add read-only cookies and host_only_cookies properties to CookieJar (and AbstractCookieJar / DummyCookieJar) so users can access stored cookies with their full attributes (expires, domain, path, etc.) without relying on private _cookies / _host_only_cookies.

• cookies returns MappingProxyType[tuple[str, str], SimpleCookie] — an immutable view of the internal cookie storage
• host_only_cookies returns frozenset[tuple[str, str]] — a frozen copy of the host-only cookie set

This addresses the long-standing request to expose cookie metadata that filter_cookies() intentionally strips (since the HTTP Cookie header does not include attributes like expires).

Are there changes in behavior for the user?

Two new public read-only properties are available on CookieJar and DummyCookieJar:

• jar.cookies — read-only mapping of (domain, path) -> SimpleCookie
• jar.host_only_cookies — frozen set of (domain, name) tuples

No existing behavior is changed.

Is it a substantial burden for the maintainers to support this?

Minimal. The properties are thin wrappers (MappingProxyType / frozenset) over existing internal state with no new data structures. The MappingProxyType prevents direct mutation of the mapping, though the underlying SimpleCookie values are still mutable — this matches the trade-off discussed in the issue.

Related issue number

Fixes #3951

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
• Add a new news fragment into the CHANGES/ folder

[codspeed-hq]

Merging this PR will not alter performance

✅ 72 untouched benchmarks
⏩ 72 skipped benchmarks¹

---

_{Comparing Br1an67:feat/expose-cookiejar-cookies (5fc4d47) with master (f69522c)}

Footnotes

1. 72 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.95%. Comparing base (f69522c) to head (5fc4d47).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #12174   +/-   ##
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  Coverage   98.95%   98.95%           
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  Files         131      131           
  Lines       46627    46688   +61     
  Branches     2418     2421    +3     
=======================================
+ Hits        46139    46200   +61     
  Misses        366      366           
  Partials      122      122           

Flag	Coverage Δ
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OS-macOS	97.93% <100.00%> (+<0.01%)	⬆️
Py-3.10	98.15% <100.00%> (+<0.01%)	⬆️
Py-3.11	98.42% <100.00%> (+<0.01%)	⬆️
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VM-macos	97.93% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	98.67% <100.00%> (-0.01%)	⬇️
VM-windows	97.03% <100.00%> (+<0.01%)	⬆️
cython-coverage	37.94% <26.98%> (-0.02%)	⬇️

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[Dreamsorcerer]

Based on @bdraco's proposal, this looks good to me. I'll let him give it final sign-off.

[bdraco]

Thanks @Br1an67

[patchback]

Backport to 3.14: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply ca9d73d on top of patchback/backports/3.14/ca9d73ddf1e2a182e058641561b7766186b30485/pr-12174

Backporting merged PR #12174 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/aio-libs/aiohttp.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.14/ca9d73ddf1e2a182e058641561b7766186b30485/pr-12174 upstream/3.14

4. Now, cherry-pick PR feat: add cookies and host_only_cookies properties to CookieJar #12174 contents into that branch:

   $ git cherry-pick -x ca9d73ddf1e2a182e058641561b7766186b30485

   If it'll yell at you with something like fatal: Commit ca9d73ddf1e2a182e058641561b7766186b30485 is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x ca9d73ddf1e2a182e058641561b7766186b30485

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR feat: add cookies and host_only_cookies properties to CookieJar #12174 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.14/ca9d73ddf1e2a182e058641561b7766186b30485/pr-12174

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
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