🎉 allow non pd.DatetimeIndex for processing

[jvdd]

Closes #125

TODO

• update processing tests (currently only checks for datetimeindex)

[codspeed-hq]

CodSpeed Performance Report

Merging #127 will improve performances by 27.86%

_{Comparing non_time_idx_processing (f8d87ea) with main (e12e550)}

Summary

⚡ 2 improvements
✅ 379 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	non_time_idx_processing	Change
⚡	test_single_series_feature_collection_multiple_descriptors[2]	1.4 s	1.1 s	+27.86%
⚡	test_single_series_feature_collection_multiple_descriptors[4]	456.3 ms	402.8 ms	+13.26%