MF6 bug: Package names should not exceed 16 characters

We should either truncate them and throw a warning, or throw an error in __setitem__ if a package key larger than 16 characters is provided.

  1. ERROR.  PACKAGENAME MUST NOT BE GREATER THAN 16 CHARACTERS.
  2. riv6 gwf1/riv-DETAILWATERLOPEN_25M.riv riv-DETAILWATERLOPEN_25M
  3. Error in PACKAGES block in file: gwf1/gwf1.nam