refactor: restructure lidarlib into xlidar-driver plugin SDK

- LidarManager facade (liblidar_manager.so): dlopen plugin discovery,
  available_drivers map<driver_id, PluginRegistry>, create_lidar_device,
  config.json load/save with legacy lidarlib migration
- Common LidarDriverInterface + DriverInfo/DeviceConfig plugin ABI
  (extern C get_driver_info / create_driver_instance)
- Plugins: driver_rplidar (ported from xlocd, Slamtec SDK), driver_olei,
  driver_sick_code (TiM CoLa-A), driver_sick_safety (nanoScan3), driver_espe
- Diagnostics extended with rplidar health + firmware; FOV filter window,
  range override and legacy remap window unified in DeviceConfig
- Rewritten README, diagnostics doc and examples (list_drivers, example,
  lidar_app)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

plugins/CMakeLists.txt

@@ -0,0 +1,29 @@
+# Driver plugins. Every plugin is a self-contained MODULE library named
+# <dir>.so (no "lib" prefix), exporting exactly the two C entry points
+# declared in include/lidar_interface.hpp. Plugins land in build/plugins/.
+
+set(XLIDAR_PLUGIN_OUTPUT_DIR ${CMAKE_BINARY_DIR}/plugins)
+set(XLIDAR_PLUGIN_COMMON_DIR ${CMAKE_CURRENT_SOURCE_DIR}/common)
+
+# xlidar_add_plugin(<name> <sources...>) — shared boilerplate for one plugin.
+function(xlidar_add_plugin name)
+    add_library(${name} MODULE ${ARGN})
+    set_target_properties(${name} PROPERTIES
+        PREFIX ""                                       # driver_olei.so, not libdriver_olei.so
+        LIBRARY_OUTPUT_DIRECTORY ${XLIDAR_PLUGIN_OUTPUT_DIR}
+        CXX_VISIBILITY_PRESET hidden                    # only the two entry points are visible
+        VISIBILITY_INLINES_HIDDEN ON
+        POSITION_INDEPENDENT_CODE ON
+    )
+    target_include_directories(${name} PRIVATE
+        ${CMAKE_SOURCE_DIR}/include
+        ${XLIDAR_PLUGIN_COMMON_DIR}
+    )
+    target_link_libraries(${name} PRIVATE Threads::Threads)
+endfunction()
+
+add_subdirectory(driver_olei)
+add_subdirectory(driver_sick_code)
+add_subdirectory(driver_sick_safety)
+add_subdirectory(driver_espe)
+add_subdirectory(driver_rplidar)