Add multi-NIC OFI/libfabric backend for Slingshot/CXI

[vinaynkaranth]

Add a libfabric (OFI) transport for MORI-IO targeting HPE Slingshot / CXI
fabrics, with per-NIC endpoint management, GPU→NIC affinity selection, and
inline descriptor-based address/MR exchange.

--- OFI backend (new) ---

• src/io/ofi/backend_impl.{hpp,cpp}: FI_EP_RDM + FI_MR_ENDPOINT + FI_MR_PROV_KEY data plane (fi_read / fi_writemsg with offset-based RMA), HMEM (FI_HMEM_ROCR)
  registration for GPU buffers with host-only fallback, inline synchronous CQ
  drain, and a background multi-CQ poller.
• Wire up the backend: src/io/engine.cpp (OFI create branch), src/io/CMakeLists.txt, include/mori/io/{backend.hpp (OfiBackendConfig), engine.hpp, enum.hpp, common.hpp},
  src/pybind/pybind_io.cpp, python/mori/io/{init.py, engine.py}.

--- Multi-NIC endpoints + affinity ---

• OfiManager opens one fabric/domain/AV/CQ/endpoint per unique provider domain (per physical NIC) from fi_getinfo, and selects the local NIC per registration
  by GPU/NUMA affinity via TopoSystem (SelectLocalNic), binding each MR to its
  chosen endpoint.
• Per-transfer destination fabric address is resolved from the remote MR's owning NIC: OfiMrBlob carries {key, nicId}; EngineDesc advertises a per-NIC
  address list (OfiEngineBlob); addresses are keyed (localNic, engineKey,
  remoteNic) since each AV is endpoint-scoped.

--- Topology: CXI NIC enumeration ---

• src/application/topology/net.cpp: enumerate HPE Slingshot (CXI) NICs from /sys/class/cxi when ibverbs finds no NICs, parsing the PCI BDF and the link
  speed from device/port/0/link/speed (e.g. ck400G → 400 Gbps). ibverbs enumeration is now fault-tolerant. (include/.../topology/net.hpp)

--- Robustness ---

• src/application/topology/system.cpp: guard null GPU / PCI-node lookups in CollectAndSortCandidates (previously segfaulted when the GPU BDF was missing
  from the PCI tree) and skip NICs absent from the tree before sorting.
• src/application/topology/gpu.cpp: minor topology load hardening.
• OfiManager::SelectLocalNic wraps affinity lookup in try/catch and falls back to a stable NIC on any topology error.

--- Tests / scripts ---

• tests/cpp/io/ofi_slingshot_test.cpp: OFI backend test.
• tests/scripts/{build_ofi_portage.sh, run_ofi_portage.sh, run_fi_write_basic.sh}: build/run harness for the OFI path.

Motivation

Technical Details

Test Plan

Test Result

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/TheRock/blob/main/GOVERNANCE.md#pull-requests.