Db api (#39731)

* first move to a db api

* mdb.spec into mdb

* mdb.u/isa -> mdb.query/isa

* mdb.u/qualify -> mdb.query/qualify

* last of mbql.u -> mbql.query and mbql.u

* remove last of the mdb.connection/db-type and use from mdb/db-type

* remove the last non-cmd usages of mdb.connection

had some circularity in

models.interface requires mdb/db-type for sql flavored "now"
mdb requires db/setup
which requires db/custom_migrations to ensure they are on cp
custom migration requires json functions in models.interface

so had to do a dynamic require for the db-type

* get db-type from mdb not mdb.env

* invoke `(mdb/app-db)` and not pass a var. lots of things fail

* mdb.setup/migrate! into mdb with potemkin

* remove get-connection. call .getConnection on the app-db

perhaps invites clumsy usage outside of `with-open` if it's a top level
function

* namespace docstrings

* last few and grab db.env/db-file into api ns

* lint cleanup

* addresses PR comments