Complete classic S7 management requests and PLC driven download

[gijzelaerr]

Summary

• Match classic S7 wire vectors for list-blocks-of-type, set clock, get block info, request download, password entry, and download responses.
• Replace the client driven download flow with the PLC driven request/response sequence in both synchronous and asynchronous clients.
• Update the Python server emulator to request bounded fragments, validate references, lengths, markers, continuation flags, and final acknowledgement, then commit the DB only after the complete transfer. Decode and validate the canonical 10-byte set-clock payload.
• Add golden packets, malformed response cases, a 40-example size property test, and sync/async 600-byte emulator transfers.

This is stacked on #903 because its response and upload validation is required. The matching Lean corpus runner update is lean-s7 #10.

Validation

• pytest -q: 1,417 passed, 52 skipped, 5 subtests passed.
• mypy snap7 s7 tests example: passed.
• uv run pre-commit run --all-files: passed.
• Lean S7 conformance corpus: 48/48 cases passed.
• Lean integration suite against the pinned python-snap7 3.0.0 emulator: passed.