The celery.shared_task decorator allows late-binding of tasks to any celery app,
which is well suited for our "task plugin" architecture.

Related T2032

Related T2032

Related T2032

Related T2032

Related T2032

Failing tests is less noisy in development mode.

Related T2032

Related T2032

Related T2032

Related T2032

Which checks the cran lister tasks written in the scheduler.

Related d30d574d
Related 5ea9d5ed

Related T2032

Relatd D2076#inline-13551

This also adds an swh-listers fixture which allows to retrieve a test ready
lister from its name (e.g gnu). Those listers have access to a scheduler
fixture so we can check the listing output from the scheduler instance.

Related D2082

Loader Task signature for the loader gnu is now:
- args:
  - package
  - package urls

- kwargs:
  tarballs: List of Dict with keys archive (unchanged), 'time' (was 'date'),
      length (new)

Prior to this commit, the code was actually duplicated with an old version
which would not work.

Related D1492#41287

Prior to this commit, the pip activation environment failed because the old cli
name no longer exists, it's named 'lister' now.

Closes T2014

Closes T2001

Previously, the Phabricator lister was disabling some loading tasks while it was not
supposed to. More precisely, due to an invalid index provided to a database query,
the latest created scheduler task was disabled each time a new page of results was
provided to the lister by the Phabricator API. Moreover, database queries were not
filtered according to the Phabricator instance resulting in possible disabling of
scheduler tasks from other instances.

Closes T2000

Without that fix, errors are raised when one wants to list Phabricator repositories
in a specific index range. The issue is due to a comparison between a string and
an integer. So convert next extracted repository index to integer to match the
corresponding model type.

Closes T1997

Turns out all newly listed repositories were filtered out because of that.
Consequently, no entries in the listers database and no scheduler loading
tasks were created when listing a Phabricator instance.

Closes T1999

Related T1984