bfastts: allow a vector for type

By default `bfastts` will fail with a cryptic message if no `type` is supplied. It should either give a reasonable message or assume `irregular` (or `regular` if #2 is implemented).

Start at the bfastts entry point and trace how a missing type is handled. Determine the expected behavior between a helpful error and assuming irregular, then verify that the no-type case no longer produces a cryptic failure; the regular default depends on issue #2.

Written by the indexing model from the issue text.