Add benchmarks for iterating multidict

[bdraco]

Iterating the multidict is a common enough operation in aiohttp that we should benchmark it
https://github.com/aio-libs/aiohttp/blob/e66b5fedc3f24d1d8c76d118b0a28df02e75e81b/aiohttp/client.py#L1082
https://github.com/aio-libs/aiohttp/blob/e66b5fedc3f24d1d8c76d118b0a28df02e75e81b/aiohttp/client_reqrep.py#L406

[codspeed-hq]

CodSpeed Performance Report

Merging #1107 will not alter performance

_{Comparing benchmark_iterate (053d9c9) with master (1ba64e7)}

Summary

✅ 184 untouched benchmarks
🆕 16 new benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
🆕	test_iterate_multidict[case-insensitive-c-extension-module]	N/A	27.8 µs	N/A
🆕	test_iterate_multidict[case-insensitive-pure-python-module]	N/A	224.7 µs	N/A
🆕	test_iterate_multidict[case-sensitive-c-extension-module]	N/A	27.9 µs	N/A
🆕	test_iterate_multidict[case-sensitive-pure-python-module]	N/A	148.8 µs	N/A
🆕	test_iterate_multidict_items[case-insensitive-c-extension-module]	N/A	48.1 µs	N/A
🆕	test_iterate_multidict_items[case-insensitive-pure-python-module]	N/A	234.9 µs	N/A
🆕	test_iterate_multidict_items[case-sensitive-c-extension-module]	N/A	47.3 µs	N/A
🆕	test_iterate_multidict_items[case-sensitive-pure-python-module]	N/A	161.6 µs	N/A
🆕	test_iterate_multidict_keys[case-insensitive-c-extension-module]	N/A	29.2 µs	N/A
🆕	test_iterate_multidict_keys[case-insensitive-pure-python-module]	N/A	220.3 µs	N/A
🆕	test_iterate_multidict_keys[case-sensitive-c-extension-module]	N/A	29.8 µs	N/A
🆕	test_iterate_multidict_keys[case-sensitive-pure-python-module]	N/A	147.9 µs	N/A
🆕	test_iterate_multidict_values[case-insensitive-c-extension-module]	N/A	27.5 µs	N/A
🆕	test_iterate_multidict_values[case-insensitive-pure-python-module]	N/A	119.8 µs	N/A
🆕	test_iterate_multidict_values[case-sensitive-c-extension-module]	N/A	28 µs	N/A
🆕	test_iterate_multidict_values[case-sensitive-pure-python-module]	N/A	114.5 µs	N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.04%. Comparing base (1ba64e7) to head (053d9c9).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1107      +/-   ##
==========================================
+ Coverage   92.96%   93.04%   +0.07%     
==========================================
  Files          44       44              
  Lines        5190     5246      +56     
  Branches      397      401       +4     
==========================================
+ Hits         4825     4881      +56     
  Misses         95       95              
  Partials      270      270              

Flag	Coverage Δ
CI-GHA	93.04% <100.00%> (+0.07%)	⬆️
MyPy	86.88% <100.00%> (+0.13%)	⬆️
pytest	100.00% <ø> (ø)

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