Feature: Add package typing marker

[JakobEliasWagner]

Feature: Add package typing marker

Description

This pr introduces support for PEP 561 to allow downstream users to leverage type hints in our library. By making this change, we provide the necessary metadata for tools like mypy to recognize and validate type hints.

Which issue does this PR tackle?

• Continuiti currently does not provide type information.

How does it solve the problem?

• Adds py.typed file that signals that Continuiti includes type information.
• Adds py.typed to the package data to ensure it is included in the package distribution.

How are the changes tested?

• All tests run without new errors.

Checklist for Contributors

• Scope: This PR tackles exactly one problem.
• Conventions: The branch follows the feature/title-slug convention.
• Conventions: The PR title follows the Bugfix: Title convention.
• Coding style: The code passes all pre-commit hooks.
• Documentation: All changes are well-documented.
• Tests: New features are tested and all tests pass successfully.
• Changelog: Updated CHANGELOG.md for new features or breaking changes.
• Review: A suitable reviewer has been assigned.

Checklist for Reviewers:

• The PR solves the issue it claims to solve and only this one.
• Changes are tested sufficiently and all tests pass.
• Documentation is complete and well-written.
• Changelog has been updated, if necessary.