The current system uses an imperative request/response model to a
communication which is full-duplex and thus (hopefully) more suited to
a reactive approach.
This updates the Chrome runner to:
* use a separate thread for reading from Chrome, which limits stalling
/ buffering
* uses futures for request/response cycles
* uses a callbacks system for events (unrequested messages from
chrome)
The test end (success / failure) is also signaled via a future.
This requires a bit more cleanup as the browser is reused for all
tests of a *class*, so e.g. the results future must be reset between
tests.
Also for convenience add debug logging of WS requests / responses,
it's convenient for looking at a test / tour's traffic.
Part-of: odoo/odoo#77735