Implement S7CommPlus V2/V3 with TLS and IntegrityId

[gijzelaerr]

Summary

• Complete V2 and V3 protocol support: TLS 1.3, per-request IntegrityId counters, session setup handshake, and password authentication (legitimation)
• Extend server emulator to fully emulate V2/V3 behavior for integration testing without real hardware
• Add async client TLS support using StreamWriter.start_tls()

Test plan

• 21 new TLS integration tests (sync + async, V2 + V3, with and without passwords)
• All 1337 existing tests pass
• mypy clean
• ruff clean

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