Replaces order-based linkage ([SerializableFieldSaveFlag]/[SerializableFieldDefault])
with field-side [SaveFlag(nameof(...))], [TimerDrift]/[DeserializeTimerField] with
[DeserializeTimer(nameof(Method), wallClock)], and documents the [SerializableField]
setter hooks (allowFieldChange/fieldChanged), the anchored-time semantics for
drifting timers, [AnchoredDateTime], and the timer MigrateFrom pattern. Narrows
[SerializableProperty] guidance to custom getters. Also fixes the documented
[SerializableField] signature (the saveIf parameter never existed) and refreshes
real-code examples that were converted in the v4 migration PRs.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>