Bug: Bad Warning in Builders

[shyamd]

MapBuilder, GroupBuilder, and ProjectionBuilder all have this ensure index warning that is not a good description of what actually went "wrong". It basically warns that one double index is missing when in fact the check is for all relevant indexes: key, last_updated and state; these are also not double indexes. Would be good to update the warning. Here is the linked code:

https://github.com/materialsproject/maggma/blob/672c6aedc8af97029b14a73849b39a9c45988e96/src/maggma/builders/map_builder.py#L79-L86