Merge branch 'release-v1.57' into develop

changelog.d/12350.bugfix

-Default to `private` room visibility rather than `public` when a client does not specify one, according to spec.
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changelog.d/12351.misc

-Remove broken and unused development scripts.
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changelog.d/12353.misc

-Convert `Linearizer` tests from `inlineCallbacks` to async.

changelog.d/12354.misc

-Update docstrings for `ReadWriteLock` tests.

changelog.d/12355.misc

-Remove broken and unused development scripts.
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changelog.d/12357.misc

-Refactor `Linearizer`, convert methods to async and use an async context manager.

changelog.d/12358.misc

-Fix a long-standing bug where `Linearizer`s could get stuck if a cancellation were to happen at the wrong time.

changelog.d/12364.bugfix

-Fix a spec compliance issue where requests to the `/publicRooms` federation API would specify `limit` as a string.
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changelog.d/12366.misc

-Make `StreamToken.from_string` and `RoomStreamToken.parse` propagate cancellations instead of replacing them with `SynapseError`s.

changelog.d/12367.feature

-Reduce overhead of restarting synchrotrons.

changelog.d/12369.doc

-Update the link to Redis pub/sub documentation in the workers documentation..
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changelog.d/12370.feature

-Update `/messages` to use historic pagination tokens if no `from` query parameter is given.

changelog.d/12371.misc

-Add type hints to tests files.
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changelog.d/12372.feature

-Reduce overhead of restarting synchrotrons.

changelog.d/12376.misc

-Allow specifying the Postgres database's port when running unit tests with Postgres.
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changelog.d/12379.misc

-Remove temporary pin of signedjson<=1.1.1 that was added in Synapse 1.56.0.

changelog.d/12380.misc

-Add opentracing spans to calls to external cache.

changelog.d/12381.misc

-Lay groundwork for using `poetry` to manage Synapse's dependencies.
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changelog.d/12384.misc

-Make missing `importlib_metadata` dependency explicit.
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changelog.d/12385.docker

-Bundle locked versions of dependencies into the Docker image.
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