IntMap.delete allocates even for absent keys

https://github.com/haskell/containers/blob/78da761ebcda243134218c062e4a9b94aaa39068/containers/src/Data/IntMap/Internal.hs#L966-L974

I noticed some code in GHC that performs a bunch of deletions (on the very similar `Word64Map`) with keys that are most likely absent from the map. So now I'm wondering whether to introduce pointer-checks in `Word64Map.delete` or to split off a `delete_possiblyAbsent` version or…

But since `Word64Map` is derived from `IntMap`, my first question is: why doesn't `IntMap.delete` perform these pointer-checks already, even though `Map.delete` does?

https://github.com/haskell/containers/blob/78da761ebcda243134218c062e4a9b94aaa39068/containers/src/Data/Map/Internal.hs#L941-L955

Compare the linked IntMap.delete implementation in containers/src/Data/IntMap/Internal.hs at lines 966-974 with Map.delete in containers/src/Data/Map/Internal.hs at lines 941-955. Start by understanding why the implementations differ and how Word64Map is derived from IntMap. Done means establishing whether pointer checks or a separate deletion variant is warranted, with the chosen scope and expected behavior clearly defined.

Written by the indexing model from the issue text.