[PR #10897/4624fed backport][3.12] Fix DNS resolver object churn for multiple sessions

[bdraco]

(cherry picked from commit 4624fed)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.16%. Comparing base (c8c3d5f) to head (82da571).
⚠️ Report is 153 commits behind head on 3.12.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##             3.12   #10906    +/-   ##
========================================
  Coverage   98.15%   98.16%            
========================================
  Files         130      130            
  Lines       39144    39282   +138     
  Branches     2218     2223     +5     
========================================
+ Hits        38423    38561   +138     
  Misses        551      551            
  Partials      170      170            

Flag	Coverage Δ
CI-GHA	98.05% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.78% <100.00%> (+<0.01%)	⬆️
OS-Windows	95.25% <100.00%> (+0.01%)	⬆️
OS-macOS	96.96% <100.00%> (+0.01%)	⬆️
Py-3.10.11	96.84% <100.00%> (+0.01%)	⬆️
Py-3.10.17	97.38% <100.00%> (+<0.01%)	⬆️
Py-3.11.12	97.44% <100.00%> (+<0.01%)	⬆️
Py-3.11.9	96.93% <100.00%> (+0.01%)	⬆️
Py-3.12.10	97.84% <100.00%> (+<0.01%)	⬆️
Py-3.13.3	97.83% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	96.72% <100.00%> (+0.01%)	⬆️
Py-3.9.22	97.26% <100.00%> (+0.04%)	⬆️
Py-pypy7.3.16	85.42% <100.00%> (-2.58%)	⬇️
VM-macos	96.96% <100.00%> (+0.01%)	⬆️
VM-ubuntu	97.78% <100.00%> (+<0.01%)	⬆️
VM-windows	95.25% <100.00%> (+0.01%)	⬆️

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[codspeed-hq]

CodSpeed Performance Report

Merging #10906 will not alter performance

_{Comparing patchback/backports/3.12/4624fed82608d9b659c4284814a570e0b332b8db/pr-10897 (82da571) with 3.12 (c8c3d5f)}

Summary

✅ 60 untouched benchmarks