Fast Async Backups

The mod has been rebuilt with the new backup strategy to fix compatibility with sable (create aeronautics & addons).

New approach — copy first, then zip:

1. saveAllChunks — Flush all chunks to disk (unchanged)
2. copyDirectory — Recursively copy the entire world folder to a temp directory using Files.copy(source, target, REPLACE_EXISTING, COPY_ATTRIBUTES) — this path-to-path copy on Windows uses the CopyFileEx API which can read locked files (unlike stream-based Files.newInputStream)
3. copyFileWithRetries — If a file is still locked, retries up to 5 times with increasing backoff (500ms, 1000ms, 1500ms, 2000ms, 2500ms)
4. zipDirectory — Zip from the temp copy (no file locks since it's our own copy)
5. deleteDirectory — Clean up the temp directory in the finally block

This ensures the backup captures the complete world including files that are locked by Sable or other mods, because the path-to-path copy operates at the filesystem level where Windows can handle shared locks. The zip step then works from our own clean copy with zero lock conflicts.