feat(historian-gateway): ContinuousHistorizationRecorder actor (outbox->WriteLiveValues, backoff)

Continuous-historization engine for non-Galaxy driver tags. Registers
interest with the per-node DependencyMuxActor for the historized refs and
taps the VirtualTagActor.DependencyValueChanged values the mux fans:
coerce to numeric -> append to the durable IHistorizationOutbox (crash
boundary) -> off-thread drain writes batches through IHistorianValueWriter
and acks (FIFO-truncates) on success, backing off (exponential, capped) on
failure. Non-numeric values are dropped + metered (SQL analog path is
numeric-only).

- New seam IHistorianValueWriter + HistorizationValue in Core.Abstractions
  so Runtime stays free of the gRPC driver.
- GatewayHistorianValueWriter (driver) adapts IHistorianGatewayClient.
  WriteLiveValues: HistorizationValue -> HistorianLiveValue proto, WriteAck
  Success||Queued -> true; non-throwing (errors -> false for retry).
- Drain runs via PipeTo(Self) so the mailbox never blocks on the gateway
  write; appends awaited on the actor thread to stay serialized.

Adaptation vs plan: the mux fans DependencyValueChanged (TagId/Value/
TimestampUtc, no quality), not DriverInstanceActor.AttributeValuePublished,
so values are recorded Good-quality (192) by the same convention the
scripted-alarm host uses.

Claude-Session: https://claude.ai/code/session_012SDSQ3AcaXqPcBtDESBRii

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/Historian/IHistorianValueWriter.cs

@@ -0,0 +1,35 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions.Historian;
+
+/// <summary>
+///     One numeric sample the continuous-historization recorder drains to the historian's SQL
+///     live-value write path. Carries the minimal payload that path can ingest: an optional UTC
+///     timestamp, the coerced numeric value, and an OPC-DA quality byte.
+/// </summary>
+/// <param name="TimestampUtc">
+///     UTC source timestamp of the sample, or <c>null</c> to defer to the historian's server-stamped
+///     current-time path (the SQL writer uses <c>SYSDATETIME()</c> when the timestamp is absent).
+/// </param>
+/// <param name="Value">The coerced numeric value (the SQL analog write path is numeric-only).</param>
+/// <param name="Quality">OPC-DA-derived quality code carried to the historian (192 = Good).</param>
+public readonly record struct HistorizationValue(DateTime? TimestampUtc, double Value, ushort Quality);
+
+/// <summary>
+///     Seam over the historian's live-value write path used by the continuous-historization recorder.
+///     Lives in the abstraction layer so the Runtime recorder depends on it without taking a hard
+///     reference on the gRPC gateway driver; the gateway driver supplies the concrete adapter
+///     (<c>GatewayHistorianValueWriter</c>).
+/// </summary>
+public interface IHistorianValueWriter
+{
+    /// <summary>
+    ///     Writes a batch of live values for a single tag through the historian's SQL live-write path.
+    ///     Implementations are expected to be non-throwing: a transport/gateway error is surfaced as a
+    ///     <c>false</c> result so the recorder retains the entries and retries, rather than as an
+    ///     exception.
+    /// </summary>
+    /// <param name="tag">Fully-qualified historian tag the values are recorded against.</param>
+    /// <param name="values">The numeric samples to write, in append order.</param>
+    /// <param name="ct">Cancellation token.</param>
+    /// <returns><c>true</c> on a successful (or durably-queued) gateway ack; <c>false</c> on a retryable failure.</returns>
+    Task<bool> WriteLiveValuesAsync(string tag, IReadOnlyList<HistorizationValue> values, CancellationToken ct);
+}