refactor(ecstore): unify remaining heal logs to structured event style (#5720)

PR #5719 fixed the issue #5716 per-object heal log amplification (per-object statements demoted, heal spans forced to TRACE, raw metadata dumps banned by guardrail) and superseded the demotion originally proposed here. This PR now carries only the residual cleanup on top of it:

- Convert the remaining bare-field and format-arg heal logs in crates/ecstore/src/set_disk/ops/heal.rs to the file's structured convention (event/component/subsystem + context fields): missing-object skip, disk-marked-for-healing, cannot-reconstruct errors, dangling-cleanup error, missing data_dir error, xl.meta regeneration warn, and orphan-reclaim failure warn.
- Demote the last remaining info! in the file — the per-set heal_format "set disk formats success, NoHealRequired" no-op message — to a structured debug! (error_count instead of a raw errs dump), and drop its whitelist exclusion in scripts/check_logging_guardrails.sh so the no-INFO check for set-disk heal files is strict.

No control flow or behavior changes.

scripts/check_logging_guardrails.sh

@@ -711,8 +711,7 @@ if [[ "$heal_function_count" != "$trace_heal_instrumentation_count" ]]; then
 fi
 
 unexpected_heal_info="$(
-  rg -n '\binfo!' crates/ecstore/src/set_disk/ops/heal.rs crates/ecstore/src/erasure/coding/heal.rs |
-    rg -v 'set disk formats success, NoHealRequired' || true
+  rg -n '\binfo!' crates/ecstore/src/set_disk/ops/heal.rs crates/ecstore/src/erasure/coding/heal.rs || true
 )"
 if [[ -n "$unexpected_heal_info" ]]; then
   echo "❌ logging guardrail violation: per-object set-disk heal events must not be emitted at INFO" >&2