run codspeed benchmarks in parallel

[jmoralez]

Description

Reduces the time to run the benchmarks by using two processes to run the tests and reducing the size of the series used.

Checklist:

• This PR has a meaningful title and a clear description.
• The tests pass.
• All linting tasks pass.
• The notebooks are clean.

[codspeed-hq]

CodSpeed Performance Report

Merging #387 will improve performances by 40.95%

_{Comparing codspeed-parallel (ed86291) with main (66fee45)}

Summary

⚡ 12 improvements

Benchmarks breakdown

	Benchmark	main	codspeed-parallel	Change
⚡	test_predict[50-1-False]	358.3 ms	254.1 ms	+41.01%
⚡	test_predict[50-1-True]	460.1 ms	309.2 ms	+48.78%
⚡	test_predict[50-2-False]	360.3 ms	255.6 ms	+40.95%
⚡	test_predict[50-2-True]	462.9 ms	310.8 ms	+48.94%
⚡	test_predict[None-1-False]	1,330.5 ms	751.5 ms	+77.06%
⚡	test_predict[None-1-True]	1,443.7 ms	818.8 ms	+76.32%
⚡	test_predict[None-2-False]	1,331.8 ms	753.6 ms	+76.73%
⚡	test_predict[None-2-True]	1,439.6 ms	821 ms	+75.34%
⚡	test_preprocess[1-False]	2.9 s	1.5 s	+97.34%
⚡	test_preprocess[1-True]	3.5 s	1.8 s	+98.42%
⚡	test_preprocess[2-False]	2.9 s	1.5 s	+97.32%
⚡	test_preprocess[2-True]	3.5 s	1.8 s	+97.45%