Update RELEASE_NOTES.md for 1.5.57-beta2 (#244)

Author: Arkatufus

RELEASE_NOTES.md

@@ -1,3 +1,16 @@
+#### 1.5.57-beta2 December 4th 2025 ####
+
+**New Features**
+* [Add semantic logging support for Akka.NET 1.5.56+](https://github.com/akkadotnet/Akka.Logger.NLog/pull/242) - NLog layouts can now access structured properties using `${event-properties:PropertyName}` syntax
+* [Support custom ILogMessageFormatter implementations](https://github.com/akkadotnet/Akka.Logger.NLog/pull/196) - Refactored NLogLogger to allow override of ILogMessageFormatter
+
+**Performance Improvements**
+* [Optimize logging of LogMessage when Parameters() is object-array](https://github.com/akkadotnet/Akka.Logger.NLog/pull/186)
+
+**Dependency Updates**
+* [Upgraded to Akka.NET v1.5.57-Beta2](https://github.com/akkadotnet/akka.net/releases/tag/1.5.57-Beta2)
+* [Upgraded to NLog v6.0.6](https://github.com/NLog/NLog/releases/tag/v6.0.6)
+
 #### 1.5.41 May 15 2025 ####
 
 * [NLogLogger - Optimize logging of LogMessage when Parameters() is object-array ](https://github.com/akkadotnet/Akka.Logger.NLog/pull/186)