fix: simplify filemeta MessagePack serialization and improve code quality

- Refactor `unmarshal_msg` to use `rmp_serde::from_slice` instead of manual parsing
- Add serde field renaming attributes to `FileMetaVersion` struct
- Remove 428 lines of manual MessagePack parsing code
- Improve string comparison using `!object.is_empty()` instead of `object != ""`
- Update volume directory numbering in run script from test{0..4} to test{1..4}
- Clean up unused imports and code

Fixes #517

ecstore/src/error.rs

@@ -851,14 +851,14 @@ pub fn error_resp_to_object_err(err: ErrorResponse, params: Vec<&str>) -> std::i
             err = std::io::Error::other(StorageError::BucketNotFound(bucket));
         }
         S3ErrorCode::NoSuchKey => {
-            if object != "" {
+            if !object.is_empty() {
                 err = std::io::Error::other(StorageError::ObjectNotFound(bucket, object));
             } else {
                 err = std::io::Error::other(StorageError::BucketNotFound(bucket));
             }
         }
         S3ErrorCode::NoSuchVersion => {
-            if object != "" {
+            if !object.is_empty() {
                 err = std::io::Error::other(StorageError::ObjectNotFound(bucket, object)); //, version_id);
             } else {
                 err = std::io::Error::other(StorageError::BucketNotFound(bucket));