Unfortunately, sphinx (actually, autodoc) only picks up attributes if
they fall in any of these cases:

1. are enum variants
2. are in slots
3. are in __dict__
4. have an annotation
5. are found using its custom parser

(see get_object_members in sphinx/ext/autodoc/importer.py)

In theory, option 5 should work for us; unfortunately, autodoc only
asks the parser the list of members with a comment.
And it's not easy to adapt it to ask the parser for all members,
because said parser (sphinx/pycode/parser.py) does not return the class
qualname (aka. namespace) for members without comments.

So, as I don't want to change the interface of sphinx.pycode.parser,
this commit switches to relying on option 3, by adding __slots__ for
all attr classes.

Additionally, this might have some performance/memory improvement
(though I did not check) and will further avoid mutation of these
objects.

All reverse dependencies have been updated to avoid using it now, so it can now
be removed, paving the way to recycle it into an intrinsic identifier.

Related to T2729

So parse_swhid raises a ValidationError when that is detected.

Related to T2769

Related to T2769

Related to T2769

Related to T2769

This avoids throwing the deprecation warning when id and target are present and
have the same value, which makes a from_dict / to_dict round-trip throw no
deprecation warnings.

This backwards-compatible change prepares the transition to give
RawExtrinsicMetadata an `id` field that is computed intrinsically from its
contents (using the HashableObject mixin).

This will enable a gradual enhancement of the functions in identifiers.py to
take model objects directly, and return the bytes of the hash instead of an
hex representation.

This collapses the shared logic between these two identifier computations into a
few more explicit steps:
 - generate data for the manifest (in either identifier computation);
 - format the manifest (in the new format_manifest function);
 - hash the manifest (in the new hash_manifest function).

This will enable reusing this logic for more object types, as well as stronger
typing for the manifest computation.

that returns a value suitable for unicity constraints.

Motivation:

* this is somewhat more of a model concern than a journal/kafka
  concern IMO
* this is one step toward adding support for non-model objects in
  KafkaJournalWriter

Implementation of the unique_key methods comes from
`swh.journal.serializers.object_key`.

I created one in the wrong directory and didn't see the existing one.

The addition of '-p no:pytest_swh_core' in pytest.ini is needed to
prevent pytest from loading the pytest_swh_core plugin which we do not
need here and which would require some more dependencies (e.g.
requests).

Use the new SWHID naming convention instead of SWH PID.

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

move most import statements in functions.

Related to T2575.

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

We may unknowingly pass naive datetimes to the storage through them,
causing the underlying DB to assign them a timezone that might not match
the actual one.

It already happens in swh.model and swh.loader.package tests.

Same as for the field data, it helps for code not yet migrated to use model
object.

Related to T645

Related to T2105

Related to T2105

Related to T2105

It can help in pytest's diffs

to fix a deprecationg warning.

to prevent warnings

D3560

 - Use dia directly to convert from .dia to .svg (inkscape would use dia via a
 plugin anyway)
 - Add proper runes to detect inkscape >= 1 and use the export options for that.

As NamedTuple inherits from tuple, msgpack serializes it like a tuple,
which makes it indistinguishable from a tuple when deserializing,
which is an issue for the RPC API.