Follow-up to https://github.com/element-hq/synapse/pull/18604
Previously, our cache metrics did include the `server_name` label as
expected but we were only seeing the last server being reported. This
was caused because we would
`CACHE_METRIC_REGISTRY.register_hook(metric_name, metric.collect)` where
the `metric_name` only took into account the cache name so it would be
overwritten every time we spawn a new server.
This PR updates the register logic to include the `server_name` so we
have a hook for every cache on every server as expected.
I noticed this problem thanks to some [tests in the Synapse Pro for
Small Hosts](https://github.com/element-hq/synapse-small-hosts/pull/173)
repo that sanity check all metrics to ensure that we can see each metric
includes data from multiple servers.
Clean up `MetricsResource`, Prometheus hacks
(`_set_prometheus_client_use_created_metrics`), and better document why
we care about having a separate `metrics` listener type.
These clean-up changes have been split out from
https://github.com/element-hq/synapse/pull/18584 since that PR was
closed.
Some small cleanups after Python3.8 became EOL.
- Move some type imports from `typing_extensions` to `typing`
- Remove the `abi3-py38` feature from pyo3
### 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))
---------
Co-authored-by: Quentin Gliech <quenting@element.io>
During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
