We only need to check it if returned bump stamp is `None`, which is rare.

Pulling this change out from one of @erikjohnston's branches
(https://github.com/element-hq/synapse/compare/develop...erikj/ss_perf)

The account data extension was also updated to avoid copies when we pull
the data out of the cache.

Fix https://github.com/element-hq/synapse/issues/17694

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This appears to be enough to make Element Web work (or at least move it
on to the next hurdle)

---------

Co-authored-by: Eric Eastwood <eric.eastwood@beta.gouv.fr>

For initial requests a typical page size is 20 rooms, so we may as well
do the batching as 20.

This should speed up bigger syncs a little bit.

Move filters tests to rest layer in order to test the new (with sliding
sync tables) and fallback paths that Sliding Sync can use.

Also found a bug in the new path because it's not being tested which is
also fixed in this PR. We now take into account `has_known_state` when
filtering.

Spawning from
https://github.com/element-hq/synapse/pull/17662#discussion_r1755574791.
This should have been done when we started using the new sliding sync
tables in https://github.com/element-hq/synapse/pull/17630

This PR changes `from pydantic import BaseModel` to `from
synapse._pydantic_compat import BaseModel` (as well as `constr`,
`conbytes`, `conint`, `confloat`).

It allows `check_pydantic_models.py` to mock those pydantic objects only
in the synapse module, and not interfere with pydantic objects in
external dependencies.

This should solve the CI problems for #17144, which breaks because
`check_pydantic_models.py` patches pydantic models from
[scim2-models](https://scim2-models.readthedocs.io/).

/cc @DMRobertson @gotmax23
fixes #17659 


### Pull Request Checklist

<!-- Please read
https://element-hq.github.io/synapse/latest/development/contributing_guide.html
before submitting your pull request -->

* [x] Pull request is based on the develop branch
* [x] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [x] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

Use Sliding Sync tables for sorting
(`bulk_get_last_event_pos_in_room_before_stream_ordering(...)` ->
`_bulk_get_max_event_pos(...)`)

Sliding Sync: Make sure we get up-to-date information from `get_sliding_sync_rooms_for_user(...)` (#17692)

We need to bust the `get_sliding_sync_rooms_for_user`
cache when the room encryption is updated and any
other field that is used in the query.

Follow-up to https://github.com/element-hq/synapse/pull/17630

- Bust cache for membership change (cross-reference
`get_rooms_for_user`)
- Bust cache for room `encryption` (cross-reference
`get_room_encryption`)
- Bust cache for `forgotten` (cross-reference
`did_forget`/`get_forgotten_rooms_for_user`)

For rooms with a name we can skip fetching a full room summary, as we
don't need to calculate heroes, and instead just fetch the room counts
directly.

This also changes things to not return counts and heroes for non-joined
rooms. For left/banned rooms we were returning zero values anyway, and
for invite/knock rooms we don't really want to leak such information
(even if some of is included in the stripped state).

For rooms with a name we can skip fetching a full room summary, as we
don't need to calculate heroes, and instead just fetch the room counts
directly.

This also changes things to not return counts and heroes for non-joined
rooms. For left/banned rooms we were returning zero values anyway, and
for invite/knock rooms we don't really want to leak such information
(even if some of is included in the stripped state).

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

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Follow-up to #17652, https://github.com/element-hq/synapse/pull/17641,
https://github.com/element-hq/synapse/pull/17634,
https://github.com/element-hq/synapse/pull/17631 and
https://github.com/element-hq/synapse/pull/17632 to fix-up
https://github.com/element-hq/synapse/pull/17512

This allows us to skip checking the database a lot of the time.

---------

Co-authored-by: Eric Eastwood <eric.eastwood@beta.gouv.fr>

When using timeline limit of 1 we end up fetching 2 events from the DB
purely to tell if the response was "limited" or not. Lets not do that.

Sliding Sync: Add comment to explain extra case where you can be invited -> banned -> unbanned (#17654)

Add comment to explain extra case where you can be
invited -> banned -> unbanned and we want to be able
to find the invite event.

Follow-up to https://github.com/element-hq/synapse/pull/17636#discussion_r1738993330

Get `bump_stamp` from [new sliding sync
tables](https://github.com/element-hq/synapse/pull/17512) which should
be faster (performance) than flipping through the latest events in the
room.