Fix bugs in syncback process and enhance error handling

- Resolved issues with nested orphan file removal, ensuring that both top-level and nested orphan files are correctly handled.
- Improved directory removal logic to gracefully handle cases where directories may have already been removed, preventing crashes.
- Enhanced the path scanning algorithm to accurately collect all source directories defined in the project, addressing missing paths in the syncback process.
- Updated logging to provide clearer debug information during directory scanning and error handling in the syncback operations.

src/syncback/fs_snapshot.rs

@@ -108,7 +108,18 @@ impl FsSnapshot {
             lock.write(base_path.join(path), contents)?;
         }
         for dir_path in &self.removed_dirs {
-            lock.remove_dir_all(base_path.join(dir_path))?;
+            let full_path = base_path.join(dir_path);
+            match lock.remove_dir_all(&full_path) {
+                Ok(()) => (),
+                // Directory might have already been removed (e.g., added twice via different code paths)
+                Err(err) if err.kind() == io::ErrorKind::NotFound => {
+                    log::debug!(
+                        "Directory already removed or doesn't exist: {}",
+                        full_path.display()
+                    );
+                }
+                Err(err) => return Err(err),
+            }
         }
         // Only remove files that aren't already inside a directory we're removing.
         // remove_dir_all already deleted those files recursively.