More often than not passing bytes to `txn.execute` is a bug (where we
meant to pass a string) that just happens to work if `BYTEA_OUTPUT` is
set to `ESCAPE`. However, this is a bit of a footgun so we want to
instead error when this happens, and force using `bytearray` if we
actually want to use bytes.
* Split state group persist into seperate storage func
* Add per database engine code for state group id gen
* Move store_state_group to StateReadStore
This allows other workers to use it, and so resolve state.
* Hook up store_state_group
* Fix tests
* Rename _store_mult_state_groups_txn
* Rename StateGroupReadStore
* Remove redundant _have_persisted_state_group_txn
* Update comments
* Comment compute_event_context
* Set start val for state_group_id_seq
... otherwise we try to recreate old state groups
* Update comments
* Don't store state for outliers
* Update comment
* Update docstring as state groups are ints
