[PR #10151/7c12b1a9 backport][3.12] Fix infinite callback loop when time is not moving forward

[patchback]

This is a backport of PR #10151 as merged into master (7c12b1a).

What do these changes do?

If the keepalive handler is called too soon, it reschedules itself. The test used now <= close_time, which means that an exactly on-time notification is treated as "too soon", causing an automatic rescheduling. For real systems the time will eventually advance and break the loop, but with async-solipsism, time doesn't advance until there is some reason to sleep and the loop is infinite.

Are there changes in behavior for the user?

This will fix infinite loops when using async-solipsism.

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

No. This does not increase the amount of code at all.

Related issue number

Fixes #10149.

Checklist

• I think the code is well written
• Unit tests for the changes exist (I am assuming that the keepalive functionality has existing test coverage)
• Documentation reflects the changes (no documentation change needed)
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      improper undesired behavior that got corrected to match
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    Fixed issue with non-ascii contents in doctest text files
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[codspeed-hq]

CodSpeed Performance Report

Merging #10174 will not alter performance

_{Comparing patchback/backports/3.12/7c12b1a9c8b2a9e33fb559229a4c4695de39f08c/pr-10151 (49f05c0) with 3.12 (99a3737)}

Summary

✅ 47 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.06%. Comparing base (99a3737) to head (49f05c0).
Report is 1 commits behind head on 3.12.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.12   #10174   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         123      123           
  Lines       37161    37182   +21     
  Branches     4469     4470    +1     
=======================================
+ Hits        36442    36463   +21     
  Misses        542      542           
  Partials      177      177           

Flag	Coverage Δ
CI-GHA	97.95% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.66% <95.45%> (+<0.01%)	⬆️
OS-Windows	94.58% <100.00%> (+<0.01%)	⬆️
OS-macOS	96.78% <95.45%> (+<0.01%)	⬆️
Py-3.10.11	96.62% <100.00%> (-0.01%)	⬇️
Py-3.10.15	97.21% <95.45%> (+0.04%)	⬆️
Py-3.11.10	?
Py-3.11.11	97.23% <95.45%> (?)
Py-3.11.9	96.70% <100.00%> (+<0.01%)	⬆️
Py-3.12.7	?
Py-3.12.8	97.72% <100.00%> (?)
Py-3.13.0	?
Py-3.13.1	97.70% <95.45%> (+0.02%)	⬆️
Py-3.9.13	96.56% <100.00%> (+<0.01%)	⬆️
Py-3.9.20	97.09% <95.45%> (-0.04%)	⬇️
Py-pypy7.3.16	96.69% <95.45%> (-0.02%)	⬇️
VM-macos	96.78% <95.45%> (+<0.01%)	⬆️
VM-ubuntu	97.66% <95.45%> (+<0.01%)	⬆️
VM-windows	94.58% <100.00%> (+<0.01%)	⬆️

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