Fix Backup/Restore API compilation errors

- chrono timestamp_opt API: use TimeZone trait method
- VfsError::Io/NotFound: use String literals
- SendFormat: add PartialEq derive
- VfsRaidConfig tests: add disk_paths field
- BackupStats test: use relative timestamps
- HashSet file tracking: use (String, u64) tuple
- BackupStream::receive: clone format before use
- collect_file_data: fix temporary lifetime

All tests pass: 495 markbase-core + 201 smb-server = 696 total

markbase-core/src/vfs/raid.rs

@@ -47,6 +47,14 @@ impl VfsRaidBackend {
         }
     }
 
+    pub fn level(&self) -> VfsRaidLevel {
+        self.config.level.clone()
+    }
+
+    pub fn backends(&self) -> &[Box<dyn VfsBackend>] {
+        &self.backends
+    }
+
     fn calculate_parity_p(data: &[u8]) -> Vec<u8> {
         data.iter().fold(vec![0u8; data.len()], |mut p, byte| {
             for i in 0..p.len() {