I cracked, and added some type definitions in synapse.storage.

Signed-off-by: Uday Bansal <43824981+udaybansal19@users.noreply.github.com>

As using non-C locale can cause issues on upgrading OS.

this saves doing it on each connection, and will allow us to pass extra options
in.

We might not need the cursor at all.

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.

Fixes #6134.

* 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

Useful when running tests when you don't care whether the server
will lose data that it claims that it has committed.

Shuffle operations so that locking upsert happens last in the txn. This ensures the lock is held for the least amount of time possible.