Fix compiler warnings: Unused function params

We could use C23's `[[maybe_unused]]` but MSVC doesn't support it.
So we void cast them with an accompanying "unused" comment.

lib/blisp.c

@@ -16,6 +16,8 @@
 static void drain(struct sp_port* port) {
 #if defined(__APPLE__) || defined(__FreeBSD__)
   sp_drain(port);
+#else
+  (void)port; // unused
 #endif
 }
 
@@ -414,4 +416,4 @@ blisp_return_t blisp_device_reset(struct blisp_device* device) {
 void blisp_device_close(struct blisp_device* device) {
   struct sp_port* serial_port = device->serial_port;
   sp_close(serial_port);
-}
+}