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/heal/data_usage_cache.rs

@@ -146,13 +146,10 @@ impl TierStats {
     }
 }
 
-#[allow(dead_code)]
-#[allow(dead_code)]
 struct AllTierStats {
     tiers: HashMap<String, TierStats>,
 }
 
-#[allow(dead_code)]
 impl AllTierStats {
     pub fn new() -> Self {
         Self { tiers: HashMap::new() }