Autosave previously froze the main thread for 2-6 seconds while
compressing the entire save file with zlib. Now the save buffer is
snapshotted under the lock (~18ms), then compression runs on a
background thread. The compressed data is committed to StorageManager
on the next main-thread tick via CommitPendingAsyncSave().
Also skip redundant full chunk saves during autosave on the dedicated
server -- chunks are already persisted by the per-tick trickle save.
Only entity data is flushed, matching Xbox/Orbis behavior.
Added per-step timing to the autosave handler for diagnostics.
itsRevela
073a511217