fix(ecstore): purge the stale destination data dir on healing rename_data commits (#5822)

* fix(ecstore): purge the stale destination data dir on healing rename_data commits

Heal commits reuse the version's existing data_dir, so when repairing
in-place corruption (bitrot) the destination directory still exists and
holds the corrupt shard files. rename(2) cannot replace a non-empty
directory (EEXIST on XFS, ENOTEMPTY on ext4), so the commit failed on
every attempt — including all scheduler retries — and in-place bitrot was
detected and reconstructed but never repaired.

Purge the stale destination data dir (move_to_trash) before the commit
rename, for healing commits only: fresh PUTs mint a new data_dir and can
never collide, and a non-healing collision keeps failing loudly. Adds the
FileInfo::is_healing() reader for the marker set_healing() already writes.

* style(ecstore): emit the heal purge failure as a structured event

The new warning was the only sentence-style log in `rename_data`'s commit
path — it sat ten lines above `info!(event = EVENT_DISK_LOCAL_RENAME_REJECTED,
component = ..., subsystem = ...)` and interpolated its values into the
message instead of carrying them as fields, so it is invisible to any operator
query keyed on `event`.

Give it the shape the rest of the file uses: a named
`EVENT_DISK_LOCAL_HEAL_PURGE_FAILED`, `component`/`subsystem`, `dst_path` and
`error` as fields, and a short label as the message. Level stays `warn` — the
purge is best effort and the rename below fails closed — and the condition,
the branch, and the control flow are unchanged.

---------

Co-authored-by: Zhengchao An <anzhengchao@gmail.com>

crates/filemeta/src/fileinfo.rs

@@ -1111,6 +1111,12 @@ impl FileInfo {
         insert_str(&mut self.metadata, SUFFIX_HEALING, "true".to_string());
     }
 
+    /// Reader for the marker [`Self::set_healing`] writes: true when this
+    /// FileInfo is being committed by the heal path.
+    pub fn is_healing(&self) -> bool {
+        contains_key_str(&self.metadata, SUFFIX_HEALING)
+    }
+
     pub fn set_tier_free_version_id(&mut self, version_id: &str) {
         insert_str(&mut self.metadata, SUFFIX_TIER_FV_ID, version_id.to_string());
     }