fix(object-data-cache): make the GET key write-unique and dedup the lookup (#4693)

fix(object-data-cache): make GET body cache key write-unique and dedup lookups

Address four object-data-cache GET-path findings (backlog#1107 batch):

ODC-06 (backlog#1111): the cache key was content-unique, not write-unique.
Extend ObjectDataCacheKey with the resolved version's modification time
(i128 unix nanoseconds, None -> 0), derived once in the shared planner so the
ecstore hook and the usecase layer produce an identical key. An unversioned
overwrite advances mod_time, so a stale node can no longer serve old bytes for
up to the TTL under an MD5 collision; etag + size stay as belt-and-braces.

ODC-16 (backlog#1121): every cacheable GET planned and looked up twice (once in
the ecstore hook, once in the usecase layer), double-counting hits, hit_bytes
and lookups. GetObjectReader now carries a GetObjectBodySource marker
(Unprobed / HookMissed / HookServed); the hook stamps it, and
build_get_object_body_with_cache serves a hook-served body directly and skips
its lookup whenever the hook already probed. One hook-served GET now records
exactly one lookup.

ODC-19 (backlog#1124): ENABLE=true with no explicit mode defaulted to HitOnly,
which never fills and keeps a permanent 0% hit rate. Default to
FillBufferedOnly, log the resolved mode at startup, and warn when HitOnly is
selected explicitly.

ODC-24 (backlog#1129): max_entry_bytes above the in-memory GET fill limits was
silently inert. Clamp the planner's size eligibility to
min(max_entry_bytes, seek-support threshold, 64 MiB buffer cap) so ineligible
sizes plan SkipTooLarge instead of being reported eligible, and warn at startup
when the excess is inert.

Co-authored-by: heihutu <heihutu@gmail.com>

crates/ecstore/src/store/init.rs

@@ -572,6 +572,7 @@ mod tests {
                 stream: Box::new(Cursor::new(self.read_payload.clone())),
                 object_info: self.object_info(bucket, object, self.read_payload.len()),
                 buffered_body: None,
+                body_source: Default::default(),
             })
         }
 

crates/ecstore/src/store/object.rs

@@ -2195,6 +2195,7 @@ mod tests {
                 stream: Box::new(Cursor::new(Vec::<u8>::new())),
                 object_info: ObjectInfo::default(),
                 buffered_body: None,
+                body_source: Default::default(),
             };
 
             let reader = ECStore::attach_read_lock_guard(reader, Some(read_guard));
@@ -2234,6 +2235,7 @@ mod tests {
                 stream: Box::new(Cursor::new(vec![1, 2, 3])),
                 object_info: ObjectInfo::default(),
                 buffered_body: None,
+                body_source: Default::default(),
             };
 
             let reader = ECStore::attach_read_lock_guard(reader, Some(read_guard));
@@ -2270,6 +2272,7 @@ mod tests {
                 stream: Box::new(Cursor::new(vec![1, 2, 3])),
                 object_info: ObjectInfo::default(),
                 buffered_body: Some(Bytes::from_static(b"123")),
+                body_source: Default::default(),
             };
 
             let reader = ECStore::attach_read_lock_guard(reader, Some(read_guard));
@@ -2306,6 +2309,7 @@ mod tests {
                 stream: Box::new(Cursor::new(vec![1, 2, 3])),
                 object_info: ObjectInfo::default(),
                 buffered_body: None,
+                body_source: Default::default(),
             };
 
             let mut reader = ECStore::attach_read_lock_guard(reader, Some(read_guard));