Accept float values for --max-fps

Android accepts a float value, there is no reason to limit the option
to be an integer.

In particular, it allows to capture at a rate lower than 1 fps. For
example, to capture 1 frame every 5 seconds:

    scrcpy --video-source=camera --max-fps=0.2

It was already possible to pass a float manually:

    scrcpy --video-source=camera \
        --video-codec-options=max-fps-to-encoder:float=0.2

But accepting a float directly for --max-fps is more convenient.

Refs <https://developer.android.com/reference/android/media/MediaFormat#KEY_MAX_FPS_TO_ENCODER>

app/src/server.c

@@ -321,7 +321,7 @@ execute_server(struct sc_server *server,
         ADD_PARAM("max_size=%" PRIu16, params->max_size);
     }
     if (params->max_fps) {
-        ADD_PARAM("max_fps=%" PRIu16, params->max_fps);
+        ADD_PARAM("max_fps=%f" , params->max_fps);
     }
     if (params->lock_video_orientation != SC_LOCK_VIDEO_ORIENTATION_UNLOCKED) {
         ADD_PARAM("lock_video_orientation=%" PRIi8,