messages: pure builders for every event the bridge sends

src/messages builds Response, StateReport, DeferredResponse, ErrorResponse, ChangeReport and the scene, doorbell
and simple events from plain values; messageId and times are parameters, so a test compares whole objects.
StateBuilder collects properties checked by the descriptors, AlexaError and AlexaErrors carry the payload fields
of an error type. AlexaStatusMessage and AlexaErrorResponse move to src/compat and are written on the builders.
On the wire, against 1.5.2: a DeferredResponse has no context key, a ChangeReport has no correlationToken, the
namespace of an ErrorResponse follows its type, and a ChangeReport without a changed property is not published:
send() resolves "" and the bridge reports an error that names the endpoint.
143 tests pass (108 before).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

dist/esm/messages/property.js

@@ -0,0 +1,15 @@
+/** A time as Alexa wants it: ISO 8601 in UTC. Text is taken as given. */
+export function isoTime(time = new Date()) {
+    return typeof time === "string" ? time : time.toISOString();
+}
+/** One property of a context or of a change, its fields in the order of the examples. */
+export function property(namespace, name, value, options = {}) {
+    return {
+        namespace,
+        ...(options.instance ? { instance: options.instance } : {}),
+        name,
+        value,
+        timeOfSample: isoTime(options.timeOfSample),
+        uncertaintyInMilliseconds: options.uncertaintyInMilliseconds ?? 0,
+    };
+}