fix: skip cache warning near end of video

Low cache is expected when the video is about to end, not a sign of
buffering issues.

scripts/playback-health.lua

@@ -139,6 +139,10 @@ local function on_cache_duration(_, duration)
     return
   end
   if duration and duration < config.cache_warning_seconds and duration > 0 then
+    local time_remaining = mp.get_property_number("playtime-remaining", 999)
+    if time_remaining < config.cache_warning_seconds * 2 then
+      return
+    end
     show_warning("cache", ("Low cache: %.1fs remaining"):format(duration))
   end
 end