fix(s7commplus): enforce async auth boundary

[gijzelaerr]

Summary

• parse async CreateObject authentication attributes with the shared parser
• reject legacy V1 SessionKey authentication before session setup with an actionable error
• document the synchronous/async V1-V3 authentication support matrix
• cover SessionKey detection and connect cleanup with mirrored async tests

Validation

• uv run pytest -q: 2125 passed, 78 skipped
• uv run pre-commit run --all-files: passed
• uv build --no-sources: passed

Fixes #836