sdk.deps: Move test depencies to extra dev section

[JGrothoff]

Move test depencies to extra dev section

Some sdk dependencies, that are only necessary for testing, are included in the mandatory dependencies.

The development dependencies can be moved to the existing optional-dependencies dev section, to make the library footprint smaller, when it is used without modifications.

I assume following deps can be moved:

• schemathesis: imported in test_http.py
• jsonschema: imported in test_http.py and test_json_serialization.py
  • used in compliance_tool --> added to pyproject.tomlin compliance_tool: add pyproject.toml #361
• hypothesis: imported in test_http.py
• types-python-dateutil: used for typechecking
• lxml-stubs: used for typechecking

[s-heppner]

Thank you very much for cleaning up these dependencies!
You are correct, the ones you moved are only necessary during development or testing.

Could you please adapt the dependency section of /sdk/README.md? (https://github.com/eclipse-basyx/basyx-python-sdk/blob/main/sdk/README.md#dependencies)
After that, we can merge this PR.

[s-heppner]

LGTM, thank you!