chore: converge stale TODOs and apply safe fills (backlog#646) (#4322)

Second TODO-convergence round over the current tree (backlog#646). All
line numbers in the old inventory had gone stale after the set_disk /
diagnostics / cluster refactors, so this re-scans and reduces the marker
count from 144 to 99.

STALE removals (comment describes already-implemented behavior, or dead
commented-out blocks) across ecstore (set_disk ops/core, store,
cluster/rpc, bucket/metadata_sys, services), iam, filemeta, s3select and
rustfs auth/object_usecase. No behavior change.

Safe fills, each verified:
- filemeta: replication_info_equals now also compares
  replication_state_internal (function currently has no callers; adds a
  regression test).
- bitrot: drop the confirmed-unused `_want` parameter from bitrot_verify
  and the now-unused `sum` on LocalDisk::bitrot_verify, removing a
  Bytes::copy_from_slice allocation. Streaming verify uses the file's
  embedded per-shard hash, never the passed sum.
- signer: rename v4_ignored_headers -> V4_IGNORED_HEADERS and drop the
  non_upper_case_globals allow.
- admin/heal: test_decode was #[ignore]d and used serde_urlencoded on a
  JSON body (would panic); rewire to serde_json::from_slice to match the
  production decode path, add assertions, un-ignore.

Verified: cargo fmt; cargo check on touched crates; tests pass
(filemeta, signer, bitrot, heal::test_decode); arch guardrail scripts
pass.

crates/ecstore/src/services/event_notification.rs

@@ -52,11 +52,6 @@ impl EventNotifier {
     }
 
     fn init_bucket_targets(&self, _api: ECStore) -> Result<(), std::io::Error> {
-        /*if err := self.target_list.Add(globalNotifyTargetList.Targets()...); err != nil {
-          return err
-        }
-        self.target_list = self.target_list.Init(runtime.GOMAXPROCS(0)) // TODO: make this configurable (y4m4)
-        nil*/
         warn!("init_bucket_targets called but currently no-op in this build");
         Ok(())
     }

crates/ecstore/src/services/rebalance/entry.rs

@@ -356,11 +356,6 @@ impl ECStore {
             "Rebalance bucket entry scan started"
         );
 
-        // TODO: other config
-        // if bucket != RUSTFS_META_BUCKET{
-
-        // }
-
         let pool = clone_arc_by_index(self.pools.as_slice(), pool_index, "invalid rebalance pool index")?;
         let bucket_configs = Arc::new(load_rebalance_bucket_configs(&bucket).await?);