Delete all empty parent directories if they are empty

This saves a lot of memory since each directory takes at least one block
We are starting to see this as an issue because the filesystems are now
much deeper due to the SE050

src/store.rs

@@ -72,7 +72,7 @@
 //! - Alternative: subdirectory <==> RP hash, everything else in flat files
 //! - In any case need to "list dirs excluding . and .." or similar
 
-use littlefs2::{driver::Storage, fs::Filesystem};
+use littlefs2::{driver::Storage, fs::Filesystem, path};
 
 use crate::error::Error;
 use crate::types::{Bytes, Location};
@@ -554,7 +554,32 @@ pub fn store(
 #[inline(never)]
 pub fn delete(store: impl Store, location: Location, path: &Path) -> bool {
     debug_now!("deleting {}", &path);
-    store.fs(location).remove(path).is_ok()
+    let fs = store.fs(location);
+    if fs.remove(path).is_err() {
+        return false;
+    }
+
+    // Only delete ancestors for volatile FS
+    if location != Location::Volatile {
+        return true;
+    }
+    // first ancestor is the file itself
+    for parent in path.ancestors().skip(1) {
+        if &*parent == path!("/") {
+            break;
+        }
+        let Ok(meta) = fs.metadata(&parent) else {
+            return false;
+        };
+        if meta.is_dir() && meta.is_empty() {
+            if fs.remove_dir(&parent).is_err() {
+                return false;
+            }
+        } else {
+            break;
+        }
+    }
+    true
 }
 
 #[inline(never)]