fix: support static cache graph replay

[gongchensu]

Update static cache writes with device-side KV caching so graph capture does not depend on host reads.

Replay static decode through paged attention using one logical block per batch while keeping the static KV layout.

Reset runtime state around capture and replay to keep graph inputs stable.

Summary

• Update static cache decode graph inputs in csrc/engine/compiler/static_batching_compiler.cpp so graph capture/replay uses stable device tensors for sequence lengths and block tables.
• Replace host-side static KV cache writes in csrc/layers/attention/backends/static_attn.cpp with device-side kv_caching_, avoiding host reads/writes during graph capture.
• Reuse paged_attention_ for static cache decode replay with one logical block per batch, while keeping the static KV cache layout unchanged.
• Reset model runtime state around warmup, capture, and replay to keep graph inputs and internal counters stable.

Motivation

Static cache graph replay could produce incorrect output because the decode path updated KV cache through host-side state and host reads, which is not graph-safe.

This PR makes static cache decode graph replay use stable device-side inputs and device-side KV cache updates, so the recorded graph can be replayed correctly without changing the static cache layout or falling back to eager execution.

Closes N/A.

Type of Change

• feat — new feature / new model
• fix — bug fix
• perf — performance improvement (no behavioral change)
• refactor — code restructuring without behavior change
• test — adding or fixing tests only
• docs — documentation only
• build / ci — build system or CI configuration
• chore — tooling, formatting, or other non-code changes
• Breaking change

Test Results of Involved Models on Supported Platforms (Please attach screenshots)

Benchmark / Performance Impact

Notes for Reviewers

CI / ChatOps

---

Checklist

Every contributor must verify every item below before requesting
review. Tick each box only after the check has actually been performed —
do not tick speculatively. If an item truly does not apply, replace the
checkbox with N/A and briefly explain why in an inline comment.

Title, Branch, and Commits

• PR title follows Conventional Commits (e.g. feat(nvidia): …, fix(cuda/gemm): …).
• Branch name follows <type>/xxx-yyyy-zzzz where <type> matches the PR title's Conventional Commits type and words are joined with hyphens (see CONTRIBUTING.md §Branches).
• Each commit message follows Conventional Commits.
• Small PR is a single squashable commit; or, for a large PR, every commit is meaningful, well-formed, and independently reviewable (see CONTRIBUTING.md §Pull Requests).
• No stray merge commits from main — the branch is rebased cleanly on top of the current main.
• No fixup! / squash! / wip commits remain.
• Existing PR/branch/commit that followed the legacy issue format.

Scope and Design

• Changes are minimal — nothing unrelated to the stated motivation was added (CONTRIBUTING.md §Code/General).
• No dead code, commented-out blocks, debug prints, printf/std::cout/print(...) left behind, or TODO without an owner and issue link.
• No unrelated formatting churn that would obscure the diff.
• Public API changes (if any) are intentional, documented, and reflected in affected callers/tests.

General Code Hygiene (applies to all languages)

• The code is self-explanatory; comments were added only where the why is non-obvious (CONTRIBUTING.md §Code/General).
• Every modified or added file ends with a single trailing newline (CONTRIBUTING.md §Code/General).
• No trailing whitespace, tab/space mixing, or stray BOMs.
• Identifiers in comments and error messages are wrapped in backticks (e.g. the `seqlens_k` tensor) (CONTRIBUTING.md §Code/General).
• All comments and error messages are in English (CONTRIBUTING.md §Code/General).
• Comments and error messages are complete sentences — capitalized first letter, terminal punctuation — unless the language/framework convention says otherwise (CONTRIBUTING.md §Code/General; §Python).

C++ Specific (if C++ files changed)

• Code follows the Google C++ Style Guide strictly.
• Error and warning message wording follows the LLVM Coding Standards (CONTRIBUTING.md §C++).
• Constructor initializer list order matches member declaration order (CONTRIBUTING.md §C++).
• No raw new/delete; RAII / smart pointers / existing allocators are used.
• Changed files are formatted by scripts/format.py.
• No changes/reference to csrc/models/llama_legacy/.

Python Specific (if Python files changed)

• Code is PEP 8 compliant.
• Comments are complete English sentences, starting with a capital letter and ending with punctuation; Markdown backticks are used for code references (CONTRIBUTING.md §Python).
• Docstrings (if any) follow PEP 257 (CONTRIBUTING.md §Python).
• Changed files are formatted by scripts/format.py.
• No changes/reference to python/infinilm/auto_config.py.

Testing

• For any platform that could not be tested, an explicit reason is given in the table and a reviewer with access has been tagged.
• Passed single request test (examples/test_infer.py), or specify the reason for skipping.
• Passed offline performance test (examples/bench.py), or specify the reason for skipping.
• Passed sanity test (test/bench/test_benchmark.py), or specify the reason for skipping.
• Passed service test (python/infinilm/server/inference_server.py + scripts/test_perf.py), or specify the reason for skipping.

Build, CI, and Tooling

• The project builds cleanly from a fresh directory on at least one affected platform.
• CI has been triggered manually (Actions → CI on this branch), or /retest was requested.

Documentation

• README.md, CONTRIBUTING.md, or inline docs updated when behavior, build flags, or developer workflow changed.
• Any user-visible breaking change is called out explicitly under "Motivation" and in the commit/PR title with a ! or BREAKING CHANGE: footer.

Security and Safety

• No secrets, access tokens, internal URLs, customer data, or personal hardware identifiers have been committed.
• Third-party code is license-compatible and attributed.
• No unsafe pointer arithmetic, uninitialized reads, or missing bounds checks were introduced.