🐛 check for None before setting n_jobs to nb logical CPUs

[jvdd]

Following the merger of #118 a bug slipped into tsflex.

Parsing the n_jobs ignored user-specified values (i.e. integers) and always selected the number of logical cores. As such, it was impossible for users to manage the number of jobs...

[codspeed-hq]

CodSpeed Performance Report

Merging #126 will degrade performances by 97.95%

_{Comparing bugfix_parse_njobs (bf1ca48) with main (577e4c2)}

Summary

❌ 2 regressions
✅ 379 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	bugfix_parse_njobs	Change
❌	test_single_series_feature_collection_multiple_descriptors[1]	483.5 ms	23,548.8 ms	-97.95%
❌	test_single_series_feature_collection_multiple_descriptors[2]	401.2 ms	1,033.1 ms	-61.17%

[jonasvdd]

The tsfel LPCC - bug - for which we provided a hotfix is fixed in tsfel>=0.1.4

https://github.com/fraunhoferportugal/tsfel/releases/tag/v0.1.4

[jonasvdd]

Ready for review @jvdd!

[jvdd]

LGTM!