Refactor logging levels to debug for improved performance and clarity

- Changed several logging statements from `info` to `debug` across various modules, including `StdBackend`, `RefPathIndex`, `ServeSession`, and `syncback_loop_with_stats`.
- This adjustment aims to reduce log verbosity during normal operations while retaining detailed logs for debugging purposes, enhancing overall performance and maintainability.

crates/memofs/src/std_backend.rs

@@ -344,7 +344,7 @@ impl VfsBackend for StdBackend {
             // This prevents a failed watch from permanently marking the path as "watched"
             match self.debouncer.watch(path, RecursiveMode::Recursive) {
                 Ok(()) => {
-                    log::info!("Watching path: {}", path.display());
+                    log::debug!("Watching path: {}", path.display());
                     self.watches.insert(path.to_path_buf());
                     Ok(())
                 }