Accept async context managers for cleanup contexts (#11681)

[MannXo]

What do these changes do?

Adapt async context managers to behave like single-yield async iterators.

1- Allow app.cleanup_ctx callbacks to return either: a single-yield async generator (existing behavior), or an async context manager (e.g. @contextlib.asynccontextmanager).

2- Internally adapt async context managers with a small adapter so: __aenter__ runs at startup (equivalent to the generator yielding), and __aexit__ runs at cleanup (equivalent to finishing the generator).

3- Preserve previous cleanup/error aggregation semantics.

Are there changes in behavior for the user?

No breaking changes; this is fully backwards compatible.

• Existing async-generator cleanup contexts continue to work unchanged.
• New: callers may pass contextlib.asynccontextmanager instances for cleanup contexts.

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

No

Related issue number

Closes #11681

Checklist

• [x] I think the code is well written
• [x] Unit tests for the changes exist
• [x] Documentation reflects the changes
• [x] If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• [x] Add a new news fragment into the CHANGES/ folder

  • name it <issue_or_pr_num>.<type>.rst (e.g. 588.bugfix.rst)

  • if you don't have an issue number, change it to the pull request number after creating the PR

    • .bugfix: A bug fix for something the maintainers deemed an improper undesired behavior that got corrected to match pre-agreed expectations.
    • .feature: A new behavior, public APIs. That sort of stuff.
    • .deprecation: A declaration of future API removals and breaking changes in behavior.
    • .breaking: When something public is removed in a breaking way. Could be deprecated in an earlier release.
    • .doc: Notable updates to the documentation structure or build process.
    • .packaging: Notes for downstreams about unobvious side effects and tooling. Changes in the test invocation considerations and runtime assumptions.
    • .contrib: Stuff that affects the contributor experience. e.g. Running tests, building the docs, setting up the development environment.
    • .misc: Changes that are hard to assign to any of the above categories.

  • Make sure to use full sentences with correct case and punctuation, for example:

    Fixed issue with non-ascii contents in doctest text files
    -- by :user:`contributor-gh-handle`.
    

    Use the past tense or the present tense a non-imperative mood, referring to what's changed compared to the last released version of this project.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #11704 will not alter performance

_{Comparing MannXo:feature/accept-async-context-manager-for-cleanup-context (5f5dd32) with master (1fbb1bb)}

Summary

✅ 59 untouched

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 98.73%. Comparing base (1fbb1bb) to head (5f5dd32). :white_check_mark: All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #11704    +/-   ##
========================================
  Coverage   98.73%   98.73%            
========================================
  Files         127      127            
  Lines       43546    43646   +100     
  Branches     2320     2323     +3     
========================================
+ Hits        42996    43095    +99     
  Misses        390      390            
- Partials      160      161     +1     

Flag	Coverage Δ
CI-GHA	98.61% <100.00%> (+<0.01%)	:arrow_up:
OS-Linux	98.34% <100.00%> (+<0.01%)	:arrow_up:
OS-Windows	96.68% <100.00%> (+<0.01%)	:arrow_up:
OS-macOS	97.56% <100.00%> (+<0.01%)	:arrow_up:
Py-3.10.11	97.11% <100.00%> (+<0.01%)	:arrow_up:
Py-3.10.18	97.61% <100.00%> (+<0.01%)	:arrow_up:
Py-3.11.13	97.81% <100.00%> (+<0.01%)	:arrow_up:
Py-3.11.9	97.32% <100.00%> (-0.01%)	:arrow_down:
Py-3.12.10	97.42% <100.00%> (+<0.01%)	:arrow_up:
Py-3.12.11	97.91% <100.00%> (+<0.01%)	:arrow_up:
Py-3.13.7	97.91% <100.00%> (-0.01%)	:arrow_down:
Py-3.13.9	97.40% <100.00%> (-0.01%)	:arrow_down:
Py-3.14.0	98.13% <100.00%> (+0.01%)	:arrow_up:
Py-3.14.0t	97.19% <100.00%> (+0.01%)	:arrow_up:
Py-pypy3.10.16-7.3.19	92.28% <100.00%> (-3.09%)	:arrow_down:
VM-macos	97.56% <100.00%> (+<0.01%)	:arrow_up:
VM-ubuntu	98.34% <100.00%> (+<0.01%)	:arrow_up:
VM-windows	96.68% <100.00%> (+<0.01%)	:arrow_up:

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