Investigation: batched content/media save on import (perf #1) (#994)

Findings doc (no code changes). Decompiled Umbraco 17.3 ContentService to
compare Save(item) vs Save(IEnumerable), and traced uSync's import scope
handling.

Conclusion: bulk Save is not a safe general win for content/media -
 - the batch overload still writes one row per item (no set-based SQL), so
   the dominant cost is unchanged;
 - its only saving (N->1 transactions + N->1 notifications) either is already
   provided by uSync's ambient suppressed scope (DisableNotificationSuppression
   = false), or, in the default config, directly conflicts with the per-item
   failure isolation that default is intentionally designed to give;
 - it also drops per-item error attribution and two validations.

Recommends leaving the (already-present but dormant) bulk hook off for
content/media and using the existing config levers instead.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: KevinJump