refactor: use pydantic for message validation

[lars-reimann]

Summary of Changes

Use pydantic to easily describe valid messages.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	5	0	0	0.82s
✅ PYTHON	mypy	5		0	2.48s
✅ PYTHON	ruff	5	0	0	0.03s
✅ REPOSITORY	git_diff	yes		no	0.02s

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e5e7011) to head (b935974).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #91   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines          750       713   -37     
=========================================
- Hits           750       713   -37     

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[lars-reimann]

🎉 This PR is included in version 0.13.0 🎉

The release is available on:

• v0.13.0
• GitHub release

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