Forbid `std::process::Command` spawning, replace with `smol` where appropriate (#38894)

std commands can block for an arbitrary duration and so runs risk of
blocking tasks for too long. This replaces all such uses where sensible
with async processes.

Release Notes:

- N/A *or* Added/Fixed/Improved ...
c69912c76aLukas Wirth committed on 9/26/2025, 3:17:36 PM· committed by GitHubparent7f14ab2
31 files changedLine totals unavailable