Harden BAT against missing/broken libraries and zstandard failures

- ExportBatPack and BAT_OT_export_zip: catch EnvironmentError (typically
  raised when zstandard is missing or the installed wheel is incompatible
  with the embedded Python) and any other exception, and report it via
  self.report instead of crashing the operator.
- file2blocks.BlockIterator: skip libraries that fail to open with a
  warning instead of aborting the whole trace, so production blends with
  one stale linked library still pack.
- preferences: use __package__ (stable, full dotted path) for the
  AddonPreferences bl_idname instead of __name__.split('.')[0], which
  breaks when the add-on is loaded under an unexpected module name.
- magic_compression: zstandard handling tweaks alongside the operator
  error reports above.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

trace/file2blocks.py

@@ -133,7 +133,11 @@ class BlockIterator:
                 continue
 
             log.debug("Expanding %d blocks in %s", len(idblocks), lib_path)
-            libfile = self.open_blendfile(lib_path)
+            try:
+                libfile = self.open_blendfile(lib_path)
+            except Exception:
+                log.warning("Failed to open library %s, skipping", lib_path, exc_info=True)
+                continue
             yield from self.iter_blocks(libfile, idblocks)
 
     def _queue_all_blocks(self, bfile: blendfile.BlendFile):