optimize applyDeletes event
- reuse set
- don't copy over again the shard ids immutable set
optimize guice injector once created

in guice, we always use eager loaded singletons for all modules we create, thus, we can actually optimize the memory used by injectors by reduced the construction information they store per binding resulting in extensive reduction in memory usage for many indices/shards case on a node

 also because all are eager singletons (and effectively, read only), we can not go through trying to create just in time bindings in the parent injector before trying to craete it in the current injector, resulting in improvement of object creations time and the time it takes to create an index or a shard on a node