Replace the cached AccountReadTime/StorageReadTime fields (which had a
snapshot-staleness bug fixed in 16e98f5d9 by re-calling Metrics()) with
a live ReadTimes() accessor. Metrics() now only returns commit/hash-phase
timings — it no longer touches atomics. blockchain.go reads atomics
directly via stateTransition.ReadTimes(), eliminating the refresh hack.
Also resolves the I1 fragility: Metrics() returning &s.metrics no longer
involves any writes inside the function, so concurrent callers can't race
on the read-time field updates.
- Add a comment at the code-mutation gate explaining the deliberate
len(code) > 0 (vs code != nil) match against non-BAL semantics; in
devnet-3 BAL access lists, an empty []byte is non-nil but encodes
"no code install".
- Remove BALStateTransitionMetrics.OriginStorageLoadTime: declared but
never assigned anywhere in the tree. The actual state-transition
read time is captured by AccountReadTime/StorageReadTime added in
the prior commit.
