remove unsafe from iter_mut#15
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What does this PR add?
unsafewe have.Details
iter_mutshows up to 15% slower performance with this change. Since it does not affectlookuporinsertit was deemed worth it just to keep the "unsafe-less" badge, for whatever it is worth.iter_mutwas unsafe as we simply keptvalues: &'a mut [V],. It's a bit annoying to prove to the compiler that our indices won't clash and therefore mut references won't alias. It would be trivial if we kept the value in theBTreeMapalong with thePrefixbut then we'd lose the contiguousness of values that helps with cache locality. Not to mention that the rest of the entry is not consulted on thelookuphot path.