chore: A/B walltime shard hang (do not merge)

[not-matthias]

Temporary draft PR: reproduces the CodSpeed walltime shard #2/#4 hang against unmodified master code on the pull_request event. Will be closed once the runs conclude.

[codspeed-hq]

Merging this PR will regress 23 benchmarks

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 16 improved benchmarks
❌ 23 regressed benchmarks
✅ 238 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	test_multiprocessing_map[1000]	3.7 MB	4.3 MB	-14.18%
❌	WallTime	test_generate_sum_of_subsets_soln[nums0-9]	26.1 µs	28.8 µs	-9.52%
❌	Memory	test_multiprocessing_map[100]	3.2 MB	3.6 MB	-9.51%
❌	WallTime	test_sum_of_squares[sum_of_squares_sum_labmda_product]	278.2 µs	302.9 µs	-8.16%
❌	WallTime	test_noop_pass_decorated	658.4 ns	706.9 ns	-6.86%
❌	WallTime	test_mmap_operation[4096]	35.9 µs	38.5 µs	-6.58%
❌	WallTime	test_multiprocessing_map[100]	52.1 ms	55.5 ms	-6.08%
❌	WallTime	test_pipe_communication[10000]	11.2 ms	11.9 ms	-6.08%
❌	WallTime	test_make_lowshelf	7.3 µs	7.7 µs	-5.42%
❌	WallTime	test_array_alloc[100]	1.1 µs	1.2 µs	-4.26%
❌	WallTime	test_mmap_operation[40960]	45.2 µs	47.2 µs	-4.22%
❌	WallTime	test_make_highshelf	7.3 µs	7.6 µs	-3.65%
❌	WallTime	test_solve_power_sum[13-2]	7 µs	7.3 µs	-3.6%
❌	WallTime	test_sleep[0.001]	1 ms	1.1 ms	-3.51%
❌	WallTime	test_tcp_connection[1.1.1.1-53]	948.1 µs	980.9 µs	-3.34%
❌	WallTime	test_generate_all_permutations[sequence1]	161.1 µs	166.4 µs	-3.18%
❌	WallTime	test_hostname_resolution[google.com]	388.5 µs	400.5 µs	-2.99%
❌	WallTime	test_tcp_connection[8.8.8.8-53]	660.8 µs	680.5 µs	-2.9%
❌	WallTime	test_solve_crossword[puzzle0-words0]	2.2 µs	2.2 µs	-2.57%
❌	WallTime	test_count_even[count_even_fast]	1.1 ms	1.1 ms	-2.51%
...	...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing scratch/walltime-hang-ab (c2fb9a5) with master (c7e9981)}