[Store] Implement dual rdma forward path

[Shichang-Zhang]

Description

This PR implements the forward transfer control path and RPC surface for Mooncake Store.

When forward mode is enabled, writes use PreWrite → RDMA write → WriteCommit and reads use PinKey → RDMA read → UnPinKey. The default reverse path (WriteRemoteData / ReadRemoteData) is unchanged unless callers explicitly select forward.

Use ReadConfigExt/WriteConfigExt (original ReadRouteConifg/WriteRouteConfig) to configure the transfer path direction。

Module

• Transfer Engine (mooncake-transfer-engine)
• Mooncake Store (mooncake-store)
• Mooncake EP (mooncake-ep)
• Integration (mooncake-integration)
• P2P Store (mooncake-p2p-store)
• Python Wheel (mooncake-wheel)
• PyTorch Backend (mooncake-pg)
• Mooncake RL (mooncake-rl)
• CI/CD
• Docs
• Other

Type of Change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation update
• Other

How Has This Been Tested?

• mooncake-store/tests/peer_client_test.cpp: PreWrite / WriteCommit / WriteRevoke, PinKey / UnPinKey (including refcount: double pin same token, double unpin, new token after full unpin), ReadRemoteData / WriteRemoteData param and error paths, not-connected RPC_FAIL cases.
• mooncake-store/tests/client_rpc_service_test.cpp: ReadRemoteData (including INTERNAL_ERROR when TE transfer is not available in fixture), PinKey / UnPinKey, existing write-path tests.
• mooncake-store/tests/p2p_client_integration_test.cpp: forward scenarios as implemented (adjust this line to match what you actually ran).

Checklist

• I have performed a self-review of my own code.
• I have formatted my own code using ./scripts/code_format.sh before submitting.
• I have updated the documentation.
• I have added tests to prove my changes are effective.

[gemini-code-assist]

Code Review

This pull request implements a forward RDMA data plane path for the Mooncake store, complementing the existing reverse path. Key changes include the introduction of a three-phase control plane (PreWrite/Pin, Transfer, and Commit/UnPin) and a lease-based resource management system within the DataManager to handle pending writes and pinned keys. Client interfaces and Python bindings have been extended to allow users to specify the RDMA direction mode. Feedback identifies a significant limitation where the forward RDMA path currently requires contiguous buffers, recommending improved documentation, more descriptive error codes, and future support for non-contiguous transfers.