Some collection types use prefix incorrectly

[abacabadabacaba]

The constructors of collection types have a parameter named prefix. A user may assume that all storage keys used to store the collection's data begin with prefix.

This doesn't hold for some collection types. This may result in storage collisions between different collections, as well as between collections and direct storage use.

Also, it will be nice if the collections in near-sdk-as had the same storage representation as in near-sdk-rs.

[willemneal]

@abacabadabacaba, which collection types does this not hold for?