Unify error messages

Ensure the result directory exists

Change action to allow purging multiple rooms

Add tests for purging

remove PurgeEventsAction

In D238#4678, @nannanko wrote:

kazv cannot be compiled with this diff.

Instead of sync forever in Client, we can do one sync cycle in the function, and give control to the user of libkazv. Then, in kazv we can implement the retry logic.

https://b.lily-is.land/#/builders/1/builds/10

mxcUri, sha256, key, iv can be combined into one object.

Fix artifacts NoneType

Use extends in CI file

Tested to work on b.lily-is.land .