[PR #8163/006fbe03 backport][3.9] Avoid creating a task to do DNS resolution if there is no throttle

[patchback]

This is a backport of PR #8163 as merged into master (006fbe0).

What do these changes do?

Avoid creating a task to do dns resolution if there is no throttle

When doing some debugging, I noticed that a large amount of tasks created on a Home Assistant instance were TCPConnector._resolve_host for cases where the host was an ip address or already in the cache. On this instance, it reduced the number of _resolve_host tasks by 99%. Previously I observed ~500 per minute.

Are there changes in behavior for the user?

There is a small performance improvement on cache hit and when the host is an ip address. Since requests no longer have to suspend on cache hit this can reduce latency of requests. Scheduling and awaiting a task on the event loop can take 2 order of magnitude more wall clock time vs running a simple function.

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

no

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (87e0697) 97.30% compared to head (5eab05d) 97.36%.

Additional details and impacted files

@@            Coverage Diff             @@
##              3.9    #8172      +/-   ##
==========================================
+ Coverage   97.30%   97.36%   +0.06%     
==========================================
  Files         108      108              
  Lines       32628    32637       +9     
  Branches     3875     3874       -1     
==========================================
+ Hits        31748    31778      +30     
+ Misses        672      655      -17     
+ Partials      208      204       -4     

Flag	Coverage Δ
CI-GHA	97.27% <100.00%> (+0.05%)	⬆️
OS-Linux	96.96% <100.00%> (+0.06%)	⬆️
OS-Windows	94.48% <100.00%> (+0.11%)	⬆️
OS-macOS	96.78% <100.00%> (+0.42%)	⬆️
Py-3.10.11	94.38% <100.00%> (?)
Py-3.10.13	96.75% <100.00%> (+0.03%)	⬆️
Py-3.11.7	96.36% <100.00%> (-0.01%)	⬇️
Py-3.11.8	96.47% <100.00%> (-0.01%)	⬇️
Py-3.12.2	96.52% <100.00%> (?)
Py-3.8.10	94.35% <100.00%> (?)
Py-3.8.18	96.68% <100.00%> (-0.01%)	⬇️
Py-3.9.13	94.37% <100.00%> (+<0.01%)	⬆️
Py-3.9.18	96.72% <100.00%> (+0.02%)	⬆️
Py-pypy7.3.15	96.27% <100.00%> (?)
VM-macos	96.78% <100.00%> (+0.42%)	⬆️
VM-ubuntu	96.96% <100.00%> (+0.06%)	⬆️
VM-windows	94.48% <100.00%> (+0.11%)	⬆️

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