Fix nlohmann_json linkage from PRIVATE to PUBLIC

Change target_link_libraries for nlohmann_json from PRIVATE to PUBLIC
since nlohmann::json types are exposed in public headers (casbin_types.h,
evaluator.h, and data_types.h). This ensures proper propagation of the
dependency to downstream consumers and prevents ABI mismatches when
multiple versions of nlohmann_json are present.

Co-authored-by: hsluoyz <3787410+hsluoyz@users.noreply.github.com>

Author: Copilot

casbin/CMakeLists.txt

@@ -77,7 +77,7 @@ add_library(casbin STATIC ${CASBIN_SOURCE_FILES})
 
 target_precompile_headers(casbin PRIVATE ${CASBIN_INCLUDE_DIR}/casbin/pch.h)
 target_include_directories(casbin PRIVATE ${CASBIN_INCLUDE_DIR})
-target_link_libraries(casbin PRIVATE nlohmann_json::nlohmann_json)
+target_link_libraries(casbin PUBLIC nlohmann_json::nlohmann_json)
 
 set_target_properties(casbin PROPERTIES 
     PREFIX ""