It enables to remove some code duplication related to git loader creation
when executing tests.

Fixes build [1]

[1] https://jenkins.softwareheritage.org/job/DVAU/job/tests/807/console

Related to T2610

Related to T2610

flake8 hook has been removed from https://github.com/pre-commit/pre-commit-hooks
so now use the one from https://gitlab.com/pycqa/flake8

by moving import statements in functions. Also simplify the main
help message to to get rid of the necessity to import swh.core.config.

Related to T2575.

instead of swh.objstorage (deprecated).

Although that will be fixed in the next version of swh-storage,
the current one returns a None status for skipped content, which
causes surprising behavior from the cooker (as it reuse the content
of the previous file in place of the current one).

Additionally, even though it shouldn't happen, if a content is
missing completely (ie. neither know nor skipped), it's still
possible to have a None status.

pytest wastes a lot of time in .hypothesis and .git; this commit excludes them.

Some tests are now failing since rDMOD6dd6acecc8297f8c9f77bdae0ccd291ceabdfd8e.

This also adds type and simplify the existing code

Related to T2105

RPCClient can handle it properly by reraising, instead of a
generic RemoteException.

Related to T2367

- blackify all the python files,
- enable black in pre-commit,
- add a black tox environment.

Also use direcly model object constructors instead of creating them from dict.

This also fixes the ci build [1]

[1] https://jenkins.softwareheritage.org/job/DVAU/job/tests/552/console

Required by swh-storage >= v0.0.172.

An ImportError was raised when one tries to start the vault server
using its CLI. Surely a side effect of recent changes in other swh
modules.

Related to D2400
Related to T2134

Allows us to call tests on things other than python3, with the same settings.

Related D2082

it has been around for months and is no longer advertized in --help string
since then

Similar to directory cooking (T1177), fetching a revision log must be performed
client-side in a paginated way to avoid storage timeouts and cooking errors.

Closes T1934