Fix compiler warnings and improve code quality

- Replace unsafe strcpy with strcpy_s for better security
- Fix DLL binding issues by adding PRIVATEBIN_API macros
- Add explicit type casts to resolve size conversion warnings
- Replace unsafe getenv with _dupenv_s for better security
- Add PRIVATEBINAPI_EXPORTS definition in CMakeLists.txt
- Improve CMake configuration for better build compatibility

CMakeLists.txt

@@ -40,6 +40,9 @@ set(HEADERS
 # Create the shared library
 add_library(privatebinapi SHARED ${SOURCES} ${HEADERS})
 
+# Define PRIVATEBINAPI_EXPORTS for the library build
+target_compile_definitions(privatebinapi PRIVATE PRIVATEBINAPI_EXPORTS)
+
 # Include directories
 target_include_directories(privatebinapi PUBLIC 
     ${CMAKE_CURRENT_SOURCE_DIR}/include
@@ -110,4 +113,4 @@ if(ENABLE_LLVM_COVERAGE)
         WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
         DEPENDS privatebinapi
     )
-endif()
+endif()