feat: add fabric-bridge node for RDMA/inter-host MXL flow sharing

- New fabric-bridge node: initiator mode reads local MXL flow and
  transfers via Fabrics (RDMA/TCP); target mode receives remote data
  and commits to local MXL flow writer
- Add set_mxl_instance/get_mxl_instance to Node base class
- CMake option DMF_BUILD_FABRICS=OFF by default (needs libfabric)
- Target publishes target_info in status for out-of-band exchange
- Initiator receives target_info via config parameter

CMakeLists.txt

@@ -14,6 +14,7 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 option(DMF_BUILD_TESTS "Build tests" ON)
 option(DMF_BUILD_MXL_TOOLS "Build MXL tools (testsrc, sink)" OFF)
 option(DMF_BUILD_DECKLINK "Build DeckLink I/O nodes" ON)
+option(DMF_BUILD_FABRICS "Build Fabrics bridge nodes" OFF)
 
 set(DECKLINK_SDK_DIR "" CACHE PATH "Path to Blackmagic DeckLink SDK root")
 
@@ -22,6 +23,11 @@ if(DMF_BUILD_DECKLINK AND DECKLINK_SDK_DIR)
     add_subdirectory(nodes/decklink-out)
 endif()
 
+if(DMF_BUILD_FABRICS)
+    set(MXL_ENABLE_FABRICS_OFI ON CACHE BOOL "" FORCE)
+    add_subdirectory(nodes/fabric-bridge)
+endif()
+
 find_package(fmt CONFIG REQUIRED)
 find_package(spdlog CONFIG REQUIRED)
 find_package(nlohmann_json CONFIG REQUIRED)