[devtools] Stop relying on Session to create connection in RepoAccess

[devtools] Stop using repo.new_session

[session] Kill support for a 'session_open' hook event To be consistent with dropping of the 'session_close' event, and also because this is already not called when using pyramid.

[devtools] Rename FakeSession into FakeConnection because it is what it is.

[cleanup] Drop references to the old internal_session method dropped a while ago, no need to talk about it in a docstring nor to fake it.

[session] Drop unused class

[cleanup] Drop no more used parse_repo_uri function

[server] Fix flake8 error of test/data/hooks.py

[repo] Drop repo.connect backward compat use new_session instead (introduced in 3.19 iirc)

[session] Drop no more necessary Session.sessionid and Connection.connectionid

[repo] Kill repo._sessions and with it the need to have a looping task to clean it up, and with that all the session's timestamping machinery.

[repo] Stop closing session The only point in "closing" session is to call the `session_close` event. Since I'm not aware of any application relying on it, I think this is too costly (in term of code) to maintain and propose to drop it.

[views] Stop giving stats / debug information relying on _sessions This is already broken when using pyramid anyway.

[session] Stop relying on _sessions to synchronize living session by doing what we currently do in pyramid. Also, attempt to synchronize CWUser's class sounds like a dark corner case handling that should be removed in favor of short lived user objects (beside it shouldn't occur except during migration).

[test] Drop useless access to repo._sessions test still succeed afterwards.

[repo] Fix flake8 errors in server/__init__.py

[repo] Drop no more used ShuttingDown exception

[repo] Drop _get_session method it's not actually necessary but holds underlying _sessions dict handling. Drop backward compat relying on it (which IMO should not be a problem). Drop import of unused QueryError along the way.

[test] Drop call to CubicWebConfiguration.load_cwctl_plugins in unittest_cwctl.py This is no longer need now that we call load_available_configurations() in the "list" command (see 5e7282bdf140).

[web] Extract a base class out WebConfiguration This will be used to build a CubicWebPyramidConfiguration in following changeset.

[tox] Drop reference to removed init_instance.py file in flake8-ok-files.txt The file got removed in 1b9fd8bda1cd.

[web] Put 'use-uicache' option in level 2 So that users do not get prompted with this. Follow-up on c34590161082.

[server] Add a "scheduler" command to run repository scheduler This commands starts the repository scheduler as a standalone process that should complement a CubicWeb web instance running as a WSGI application. Added a log message in repository's shutdown method to help testing the command (i.e. make sure the method is called after the scheduler stopped). Related to #17057223.

[cwconfig] Do not instantiate a repo with a scheduler in repository method None of the caller of this method need the repository to have a scheduler and having a scheduler should be something that's explicitly requested.

[server] Make cubicweb/server/utils.py flake8-clean

[server] Drop utils's LoopTask and TasksManager classes not used anymore Related to 17057223.

[server] replace repository's tasks manager by a scheduler Repository() does not accept anymore a 'tasks_manager' argument but rather a 'scheduler' argument which is expected to be an instance of sched.scheduler class. The drop the _tasks_manager attribute of the repository and adjust all internal usages of it. In particular, in the 'repo_stats' service we do not export 'looping_tasks' statistics anymore as there's no way to retrieve this anymore from a web instance. Closes #17057223.

[server] introduce a scheduler class to run repository "looping tasks" We just use the sched module from the standard library and introduce a tiny Python2/3 compatibility layer (more for convenience actually). The "looping" aspect of tasks (previously in LoopTask class) is re-implemeted as a `schedule_periodic_task` function. This is a reasonably thin layer as compared to LoopTask/TasksManager classes. Only the "restart" aspect of LoopTask is no longer present as I'm not sure it's worth keeping. The advantage of using this (in addition to eventually dropping our custom code) is that this scheduler class provides a `run` method that blocks the process while running tasks in its queue. So we can rely on this to have a 'scheduler' ctl command (see forthcoming patch) that would only run "looping tasks" without having to implement the "blocking" aspect ourself. Related to #17057223.

web: add options to ignore css compilation and uicache

[skeleton] call includeme from new cube