[PR #6547/65de218c backport][3.15] Remove overlapping slots and fix broken slots inheritance

[webknjaz]

This is a (manual) backport of PR #6547 as merged into master (65de218).

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(looks like what's left is running that slotscheck linter which got lost and is now failing for whatever reason!?)*

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.66%. Comparing base (7977dcf) to head (3011858).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.15   #13466   +/-   ##
=======================================
  Coverage   95.66%   95.66%           
=======================================
  Files         160      160           
  Lines       51183    51183           
  Branches     2828     2828           
=======================================
  Hits        48964    48964           
  Misses       2039     2039           
  Partials      180      180           

Flag	Coverage Δ
CI-GHA	95.63% <ø> (-0.01%)	⬇️
OS-Linux	95.41% <ø> (-0.01%)	⬇️
OS-Windows	93.15% <ø> (-0.01%)	⬇️
OS-macOS	94.59% <ø> (ø)
Py-3.10	94.76% <ø> (ø)
Py-3.11	95.04% <ø> (-0.01%)	⬇️
Py-3.12	95.12% <ø> (ø)
Py-3.13	95.11% <ø> (+<0.01%)	⬆️
Py-3.14	95.20% <ø> (ø)
Py-3.14t	94.21% <ø> (-0.01%)	⬇️
Py-pypy-3.11	94.07% <ø> (-0.01%)	⬇️
VM-macos	94.59% <ø> (ø)
VM-ubuntu	95.41% <ø> (-0.01%)	⬇️
VM-windows	93.15% <ø> (-0.01%)	⬇️
cython-coverage	78.04% <ø> (ø)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 84 untouched benchmarks
⏩ 86 skipped benchmarks¹

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_{Comparing webknjaz:patchback/backports/3.15/65de218c6297284663eeae5c07e9146ef1e4485e/pr-6547/handcrafted-cherry-pick-by-webknjaz (3011858) with 3.15 (7977dcf)}

Footnotes

1. 86 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. ↩

[webknjaz]

https://github.com/aio-libs/aiohttp/actions/runs/32053849820/job/95459534867?pr=13466#step:9:51:

stats:
ERROR: 'aiohttp.web_routedef:RouteDef' defines slots but superclass does not.
  modules:     55
    checked:   54
    excluded:  1
    skipped:   0

  classes:     302
    has slots: 247
    no slots:  55
       Superclasses without slots:
       - 'aiohttp.web_routedef:AbstractRouteDef'
ERROR: 'aiohttp.web_routedef:StaticDef' defines slots but superclass does not.
       Superclasses without slots:
       - 'aiohttp.web_routedef:AbstractRouteDef'
Oh no, found some problems!