feat(auditlog): hot-reloadable AuditLogOptions + regex cache invalidation (#23 M5)

src/ScadaLink.AuditLog/Payload/DefaultAuditPayloadFilter.cs

@@ -22,7 +22,13 @@ namespace ScadaLink.AuditLog.Payload;
 /// <para>
 /// Uses <see cref="IOptionsMonitor{TOptions}"/> (not <see cref="IOptions{TOptions}"/>)
 /// so the M5-T8 hot-reload path sees fresh values without re-resolving the
-/// singleton.
+/// singleton. <see cref="Apply"/> reads <see cref="IOptionsMonitor{T}.CurrentValue"/>
+/// on every call, and the regex cache is keyed by pattern string — patterns
+/// added via a live config change compile on first use of the next event;
+/// patterns removed simply stop being looked up. No <c>OnChange</c> subscription
+/// or explicit cache invalidation is required (the
+/// <c>AuditLogOptionsBindingTests</c> fixture in <c>ScadaLink.AuditLog.Tests</c>
+/// pins this behaviour).
 /// </para>
 /// <para>
 /// "Error row" = <see cref="AuditEvent.Status"/> NOT IN (<c>Delivered</c>,