Fix infinite `iter_chunks()` on empty response

[agners]

What do these changes do?

When aiohttp returns an empty reader, the first time the iter_chunks() iterator stops after the first read as expected. However, on the second empty reader return, iter_chunks() loops forever.

This is due to state sharing caused by the global EmptyStreamReader instance. It has been noticed during review in #7645, but so far hasn't been addressed.

This PR attempts to address the issue by returning a new instance.

Are there changes in behavior for the user?

The change makes it safe to read content of empty responses using iter_chunks().

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

Related issue number

Checklist

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• [ ] Unit tests for the changes exist
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[agners]

This came up in Home Assistant Core PR https://github.com/home-assistant/core/pull/147899. The PR now avoids reading empty responses as a work around. /cc @bdraco

[codecov[bot]]

Codecov Report

:x: Patch coverage is 80.64516% with 6 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 98.74%. Comparing base (48082a7) to head (c08dce1). :warning: Report is 73 commits behind head on master. :white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
tests/test_streams.py	76.92%	4 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11397      +/-   ##
==========================================
- Coverage   98.76%   98.74%   -0.02%     
==========================================
  Files         129      129              
  Lines       43416    43444      +28     
  Branches     2324     2328       +4     
==========================================
+ Hits        42879    42899      +20     
- Misses        383      388       +5     
- Partials      154      157       +3     

Flag	Coverage Δ
CI-GHA	98.63% <80.64%> (-0.02%)	:arrow_down:
OS-Linux	98.36% <80.64%> (-0.02%)	:arrow_down:
OS-Windows	96.78% <80.64%> (-0.03%)	:arrow_down:
OS-macOS	97.67% <80.64%> (-0.02%)	:arrow_down:
Py-3.10.11	97.30% <74.19%> (-0.03%)	:arrow_down:
Py-3.10.18	97.70% <74.19%> (-0.03%)	:arrow_down:
Py-3.11.13	97.90% <74.19%> (-0.03%)	:arrow_down:
Py-3.11.9	97.50% <74.19%> (-0.04%)	:arrow_down:
Py-3.12.10	97.60% <74.19%> (-0.04%)	:arrow_down:
Py-3.12.11	98.00% <74.19%> (-0.02%)	:arrow_down:
Py-3.13.5	98.25% <74.19%> (-0.03%)	:arrow_down:
Py-3.9.13	97.19% <80.64%> (-0.03%)	:arrow_down:
Py-3.9.23	97.60% <80.64%> (-0.02%)	:arrow_down:
Py-pypy7.3.16	86.76% <74.19%> (-5.68%)	:arrow_down:
VM-macos	97.67% <80.64%> (-0.02%)	:arrow_down:
VM-ubuntu	98.36% <80.64%> (-0.02%)	:arrow_down:
VM-windows	96.78% <80.64%> (-0.03%)	:arrow_down:

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[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #11397 will not alter performance

_{Comparing agners:fix-infinte-iter-chunks-on-empty-response (c08dce1) with master (48082a7)}

Summary

✅ 59 untouched benchmarks