Related to T2961

The optional nature of the type will allow to avoid migrating the
(db) data model right now then we can have this type field in kafka
messages in the origin-visit-status topic

Related to T2443

Related to T2610

Add a new extra_headers attribute on Revision and use it for computing
the revision's id instead of extract it from the metadata field.

Only accept (bytes, bytes) as extra_header.

Add a post init hook to Revision to initialize this new attribute from
given metadata, if any, for bw compat.

Also amend the revision_d hyptothesis strategy to generate extra_headers.

Related to T2310

Related to T2310

Related to T2310

This is not used. This is broken storage wise (origin-visit-add does not deal
correctly with it and it so happens there is no test around it).

And finally, this will soon go away with T2310.

And adapt the revisions_d() strategy accordingly.

This can be None, according to the model.

for the sake of consistency.

This is a step forward having model objects, declared as frozen, immutable.

This requires attrs_strict >= 0.0.7.

the visit attribute is expected to be strictly positive.

Simply add a BaseModel.anonymize() method. Default implementation returns
None, meaning the object is not anonymizable.

For Person, the method returns a Person whith hashed fullname (and unset
name and email).

For Revision and Release, the method returns an anonymized version of
the object, i.e. with instance of Person replaced by anonymized ones.

Production should only use aware datetimes.

Make it possible to generate Content and SkippedContent under different
object types (namely "content" and "skipped_content").

Default to False to keep backward compat.

so one can choose not to generate some of the object types.

Blacklist "origin_visit_status" by default to prevent breaking dependent
packages' tests.

This also adapts the hypothesis strategies, using the plural form
origin_visit_statuses. That plural form is acceptable because in our context,
the statuses are countable.

Related to T2310

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

Fix keyword parameters transmission to snapshots_d strategy.

Ensure max_size constraint is respected when fixing snapshot aliases.

With support for str representation of date.
Mostly for testing purpose.

for each entity model `Model`, provide a `models_d` strategy that
produces dicts suitable for using as argument for the `Model.from_dict`
factory method, and reimplement the `models` generator using this
former hypothesis generator.

This is needed to help writing low level tests for model entities.

- add a validator for negative_utc (can be True iff offset is 0),
- update the timestamps_with_timezone hypothesis strategy,
- add low-level tests for it.

(pairing with @vlorentz)

Related to T2310

it was still here for bw-compat but should not be necessary any more.

This generates more realistic contents and avoids spurious HashCollisions when
generating a set of objects using these hypothesis strategies, at the cost of
slightly worse "boundary checking" (i.e. we won't check contents with a length >
4096 bytes).

It already is in practice.

The current postgresql model refuses NULL values.

Add support to automatically compute identifier in the following object models:
Directory, Release, Revision, Snapshot.

If the identifier is not provided as parameter, it will be computed when the model
is initialized.

we do not really need them to be mutable, plus we gain their instances now
being hashable, so we can add them in set() for example.