ci: investigate Mac & Windows pipelines perf differences respect to Linux

For some reason, it seems that Windows & Mac pipelines are much slower than those of Linux. It would be interesting to investigate what's behind that difference, and try to solve it if possible.

The issue names no files, tests, or pipeline entry points. Start by comparing the Mac, Windows, and Linux pipeline runs to identify where their times diverge; done means the cause is documented and any proposed fix is validated across the affected platforms.

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