Before this change, a Directory object was built to compute the `id` of
we fed to the Directory object we built for `to_model`.

We tested this change on simple information of the Mercurial loader,
with a noop-loader stockage:

    swh loader run mercurial https://foss.heptapod.net/mercurial/mercurial-devel directory=/data/repos/mercurial-devel

= Median time of 3 run =
before: 17 minutes 48 seconds
after:  12 minutes 59 seconds

On a profile of the same run, the `to_model` call of the from_disk's `Directory` class took the following percentage:
before: 43%
after:  24%

Format was changed in 752fb81d.

This is needed by swh-scrubber when recomputing the hash of such snapshots.

It allows building a snapshot manifest despite some branches being
unresolved (instead of raising an error).

This feature was removed in 57ae405d
but in the end, Snapshot.compute_hash() will need to use it so that
swh-scrubber does not crash when checksum such snapshots.

hypothesis.strategies.integers() is inclusive, but microseconds values
greater or equal to 1 million are rejected by the model

This allows callers to pass different (typically, stricter) strategies
to hypothesis instead of filtering the output; which makes example
generation faster.

It will be used by swh.storage.backfiller (so indirectly, swh.scrubber)
to load directories from the postgresql database, whose schema accidentally
allowed directories with duplicate entries -- without corrupting the
shape of the directory too much.

We can use `format_git_object_from_parts` inside it.

This would be useful for the IPFS bridge, and seems good to complete the
API in any sense.

That hook can be frustrating as it can discard a long commit message
if it finds a typo in it so better removing it.

it's a piece of information used several times in the swh stack.

Related to T3922

black is considered stable since release 22.1.0 and the version
we are currently using is quite outdated and not compatible with
click 8.1.0, so it is time to bump it to its latest stable release.

Please note that E501 pycodestyle warning related to line length
is replaced by B950 one from flake8-bugbear as recommended by black.
https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#line-length

Related to T3922

Hypothesis: This makes the documentation build fail.

This changes the deprecated :show-nested: instruction to the :nested: one [1].
This also fixes warning about misdefined block [2]

[1] https://sphinx-click.readthedocs.io/en/latest/usage/#directive-click

[2]
```
10:38:38  Warning, treated as error:
10:38:38  /var/lib/jenkins/workspace/DMOD/tests-on-diff/docs/cli.rst:14:Literal block expected; none found.
10:38:38  make: *** [../../swh-docs/Makefile.sphinx:32: sphinx/html] Error 2
10:38:38  make: Leaving directory '/var/lib/jenkins/workspace/DMOD/tests-on-diff/docs'
10:38:38  ERROR: InvocationError for command '/usr/bin/make -I ../.tox/sphinx/src/swh-docs/swh/ -C docs' (exited with code 2)
```

committer=None happens on some malformed commits generated by old dgit
versions ; and it is possible for author=None to happen for the same reason.

Due to test modules being copied in subdirectories of the
build directory by setuptools, it makes pytest fail by raising
ImportPathMismatchError exceptions when invoked from root
directory of the module.

So ignore the build folder to discover tests.

these fields are computed attributes and may be removed from the backend
storage. Helps writing tests.

This will be used by swh.storage.backfill's tests.

This reverts commit a0f54362.

This means this commit removes the 'offset' and 'negative_utc'
arguments.

It also removes the 'negative_utc' attribute (which is not used
anymore), but keeps an 'offset' property, which is an alias to
'offset_minutes()'. This is only to keep this commit readable;
the next commit will remove this alias.

To install the new hook:

  $ pre-commit install -t commit-msg

This should slightly reduce the memory used by dir/rev/rel objects

A future commit will remove the 'offset' attribute, and rename
'offset_bytes' to 'offset'.

Modules using the `.offset` attribute will need to switch to this new
method to keep working.

Sphinx >=4.4.0 raises warnings (which are errors for us) when using
warnings instead of an extlink role defined in the configuration