watched files seems to not get released

[kares]

from input's internal FileWatch::WatchedFilesCollection, the collection removes entries on errors
but seemingly (in read mode) when a file is processed and deleted the WatchedFile bits stays around.

collection will tend to grow, until LS is restarted, proportionally to the number of entries (over-time) in a directory. e.g. ~ 70k files coming and going in a directory will retain ~ 150MB of heap for the collection.

we need to look into releasing (deleted) file entries from the watcher to reduce memory use ... in some cases this might be clearly considered a potential leak.