[None][feat] Merge back DeepSeek V4 cache manager updates

[jiaganc]

@coderabbitai summary

Description

Merge back the PR1 DeepSeek V4 cache-manager work onto current main.

This includes DeepSeek V4 sparse cache-manager updates, KVCacheManagerV2
adaptations after its migration from resource_manager.py to
kv_cache_manager_v2.py, disaggregated KV-transfer/cache-reuse updates,
iteration stats reporting, OpenAI serving metrics updates, and rebase
compatibility fixes needed on top of current main.

This PR is opened as a draft because selected changed tests were intentionally
skipped by request and broader CI/build validation can still run before review.

Test Coverage

Remote unit tests were run on umb-b300-dp-186 inside container
trtllm-main-dsv4-cache-manager-mergeback-round2-jenkins-jiaganc at SHA
e188f8076c.

Passed:

python3 -m pytest -q \
  tests/unittest/llmapi/apps/test_disagg_perf_metrics_collector.py \
  tests/unittest/llmapi/apps/test_openai_server_iteration_stats.py \
  tests/unittest/disaggregated/test_openai_disagg_service.py \
  tests/unittest/disaggregated/test_cache_reuse_adapter.py \
  tests/unittest/kv_cache_manager_v2_tests/test_kv_cache_stats_behavior.py \
  tests/unittest/llmapi/test_llm_args.py

Result: 283 passed, 3 skipped, 4 warnings in 129.98s

python3 -m pytest -q \
  tests/unittest/_torch/attention/sparse/deepseek_v4/test_compressor_module.py \
  tests/unittest/_torch/attention/sparse/deepseek_v4/test_deepseek_v4_cache_manager.py

Result: 149 passed, 4 warnings in 71.21s

python3 -m pytest -q \
  tests/unittest/disaggregated/region/test_page.py \
  tests/unittest/disaggregated/region/test_region.py \
  tests/unittest/disaggregated/test_cache_transceiver_single_process.py \
  tests/unittest/disaggregated/test_deepseek_v4_kv_transfer.py \
  tests/unittest/disaggregated/test_extractor.py \
  tests/unittest/disaggregated/test_kv_transfer.py \
  tests/unittest/disaggregated/test_peer.py \
  tests/unittest/disaggregated/test_pool_matching.py

Result: 392 passed, 66 skipped, 4 warnings in 146.77s

python3 -m pytest -q \
  tests/unittest/kv_cache_manager_v2_tests/test_kv_cache_manager_v2.py

Result: 63 passed, 12 skipped, 5 warnings in 338.84s

Skipped by request:

• executor tests
• tests/unittest/_torch/modeling/test_modeling_deepseekv4.py
• tests/unittest/_torch/attention/sparse/deepseek_v4/test_deepseek_v4_indices_transform.py
• tests/unittest/_torch/attention/sparse/deepseek_v4/test_deepseek_v4_sparse_mla.py
• tests/unittest/_torch/speculative/test_eagle3.py

PR Checklist

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• Update tava architecture diagram if there is a significant design change in PR.

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• Please check this after reviewing the above items as appropriate for this PR.

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