Reasons:
- Only parallelized piece of code gives little local speedup (code block only about 25% quicker even on 1M polys cube).
- No gain nor loss using new BLI_task system.
- At 10% of build, parallelized piece of code is only about 5% of total func runtime (run-time explodes as build proportion increases).
See no point in adding (in utmost best optimistic case, in real use-case, when depsgraph will likely already fire several evaluations in parallel,
speedup would be even smaller) 1% speedup here at the cost of threading complexity...
Note that since later code uses hashes, I don't think it's easy to thread it, so think we can leave with it for now.
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