Make ctest build and run on Windows in addition to Linux/macOS:
- Add OS detection in Makefile using ifeq ($(OS),Windows_NT)
- Use .lib extension and .exe suffix on Windows
- Link Windows system libraries (winmm, ws2_32, ole32)
- Remove unused dlfcn.h include that prevented compilation on Windows
Fix memory management to use RcloneFreeString instead of free for
strings returned by RcloneRPC, as documented in the librclone README.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
