WebDAV additional fixes: dead props compaction + accessed metadata

- save_props/patch_props: filter empty entries before persisting
- VfsDavMetaData: add accessed field + accessed() method

Tests: 288 passed, 0 failed

markbase-core/src/webdav.rs

@@ -127,6 +127,7 @@ impl VfsDavFs {
         };
         let entries: HashMap<String, Vec<DeadPropEntry>> = data
             .iter()
+            .filter(|(_, v)| !v.is_empty())
             .map(|(k, v)| (k.clone(), v.iter().map(DeadPropEntry::from).collect()))
             .collect();
         if let Ok(json) = serde_json::to_string(&entries) {
@@ -229,14 +230,17 @@ pub struct VfsDavMetaData {
     len: u64,
     is_dir: bool,
     modified: SystemTime,
+    accessed: SystemTime,
 }
 
 impl VfsDavMetaData {
     pub fn new(len: u64, is_dir: bool) -> Self {
+        let now = SystemTime::now();
         Self {
             len,
             is_dir,
-            modified: SystemTime::now(),
+            modified: now,
+            accessed: now,
         }
     }
 
@@ -245,6 +249,7 @@ impl VfsDavMetaData {
             len: stat.size,
             is_dir: stat.is_dir,
             modified: stat.mtime,
+            accessed: stat.atime,
         }
     }
 }
@@ -261,6 +266,10 @@ impl DavMetaData for VfsDavMetaData {
     fn is_dir(&self) -> bool {
         self.is_dir
     }
+
+    fn accessed(&self) -> Result<SystemTime, FsError> {
+        Ok(self.accessed)
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -814,6 +823,7 @@ impl DavFileSystem for VfsDavFs {
                     }
                 };
                 map.iter()
+                    .filter(|(_, v)| !v.is_empty())
                     .map(|(k, v)| (k.clone(), v.iter().map(DeadPropEntry::from).collect()))
                     .collect()
             };