chore: Bump actix-web version to 4.0 (stable)

[Chaostheorie]

Description:

Bump Actix Web dependency to stable 4.0 and add macros feature to support get, ….

Closes #31

Checklist:

• [x] Tests for the changes have been added (for bug fixes / features);
• [x] Docs have been added / updated (for bug fixes / features).
• [x] This PR has been added to CHANGELOG.md (to [Unreleased] section);

[DDtKey]

Thank you for your help! 🚀 I'll release the new version soon 🙂