✨ Adopt PEP 735 dependency groups

[burgholzer]

Description

This PR updates the project to use the dependency groups feature that was proposed in PEP 735 and is available in uv since 0.4.27 in favour of optional dependencies.
It adds three explicit dependency groups:

• build, containing the build time dependencies,
• test, containing the test dependencies (including coverage), and
• docs, containing the docs dependencies.

In addition,

• enables testing on Python 3.13 (after some dependency adjustments),
• updates lower bounds for many development dependencies, and
• refactors the nox sessions as well as the RtD script to take advantage of the new dependency groups.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.