We did this already for local `/keys/upload` but didn't for
remote `/users/devices`. This meant any resyncs would spam produce
events, hammering disk i/o and spamming the logs.
* WIP: Eagerly sync device lists on /user/keys/query requests
Also notify servers when a user's device display name changes. Few
caveats:
- sytest `Device deletion propagates over federation` fails
- `populateResponseWithDeviceKeysFromDatabase` is called from multiple
goroutines and hence is unsafe.
* Handle deleted devices correctly over federation
* Add sync mechanism to block when updating device lists
With a timeout, mainly for sytest to fix the test
"Server correctly handles incoming m.device_list_update"
which is flakey because it assumes that when `/send` 200 OKs
that the server has updated the device lists in prep for
`/keys/query` which is not always true when using workers.
* Fix UT
* Add new working test
* Add tests for device list updates
* Add stale_device_lists table and use db before asking remote for device keys
* Fetch remote keys if all devices are requested
* Add display_name col to store remote device names
Few other tweaks to make `Server correctly handles incoming m.device_list_update`
pass.
* Fix sqlite otk bug
* Unbuffered channel to block /send causing sytest to not race anymore
* Linting and fix bug whereby we didn't send updated dl tokens to the client causing a tightloop on /sync sometimes
* No longer assert staleness as Update blocks on workers now
* Back out tweaks
* Bugfixes
