Adapt DeepSeek persistent worker to offset cache copies

[high-cloud]

Summary

• Upload dirty DeepSeek decode work-cache pages through a base allocation plus byte offset instead of passing an interior device pointer to copy_to.
• Keep the DeepSeek shared L3 worker persistent and rely on the corresponding PyPTO default of reset_persistent_windows=False, so serving does not perform a host-side comm-window reset between requests.

Root cause

The latest simpler device-pointer provenance guard requires copy_to to receive the base address of a live allocation. DeepSeek work-cache synchronization previously passed shard.data_ptr + offset, which is an interior pointer and is rejected before prefill starts.

Dependencies

This PR depends on:

• PyPTO #2164, which adds DistributedWorker.copy_to_offset(...);
• simpler #1538, which adds Orchestrator.copy_to_offset(...) and validates the live base allocation before applying the byte offset;
• PyPTO #2163, which makes reset_persistent_windows=False the persistent-worker default.

Validation

• python -m pytest -q tests/test_deepseek_v4.py — 32 passed.
• ruff check --config ruff.toml pypto_serving/model/deepseek/npu_runner.py — passed.
• python tests/lint/check_headers.py — passed.
• python tests/lint/check_english_only.py — 53 passed.
• python -m compileall -q pypto_serving/model/deepseek/npu_runner.py — passed.
• 8-card DeepSeek V4 MTP accuracy: task_20260727_032719_85546414704 — 4 passed, serving shut down normally, and profiling trace was written to artifacts/forward-end-clear-mtp-v2/trace.json.

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