Guard against sending any queries for unpersisted models

@trobrock

Mimics AR and acts_as_paranoid (R2) behavior on unpersisted models, in that it doesn't query the DB on delete. Still to do:
- Tests for this case: I tried ActiveRecord::TestCase#assert_no_queries, but it appears to not work as advertised
- Support callbacks on unpersisted models - changes here go a little deeper.

This should at least address our rogue workling queries ("is_deleted = 1" * 100).