GitLab

Don't require 'immutables' but use it if installed.

See merge request !24

See https://github.com/MagicStack/immutables/issues/77

Remove dependency 'typing_extensions' and improve type hints.

See merge request merchise-autrement/xotless!2

typing_extensions is no longer needed since we support only Python 3.8+ which
already has typing.Protocol and typing.runtime_checkable.

Apparently that's preventing tox from creating the environments in shared CI
environments and failing.

We don't have too many runners, so running all tests in parallel could make
generation of samples slower and prone to failure.

This will allow us to know if the Sentry SDK could fail when installed.

This will allow the introduction of a unified API `IntervalTree` while we
might introduce different implementations (for instance, I will need one with
closed intervals).

We getting issues of too-slow generation of samples.  Of course we should try
to fix the generation of intervals, but I don't have much time now for this.

At the same run doctests, coverage, etc in Python 3.10 which has gained some
speed improvements, this might help with this issue.

Add support for Python 3.10

See merge request !21

Update mypy and black.

See merge request !20

This seems to have an impact in the performance of the strategies, causing a
FailedHealthCheck.

At the same, try to isolate the CI job that checks coverage, to avoid slowing
down because of a busy Gitlab Runner.