Update RELEASE_NOTES.md for 1.5.57-beta2 release

[Arkatufus]

1.5.57-beta2 December 3rd 2025

• Update Akka.NET to 1.5.57-beta2
• Add semantic logging support for Akka.NET 1.5.56+

This release adds full semantic logging support, enabling Serilog to receive properly structured message templates and parameters instead of pre-formatted strings. This enhancement leverages Akka.NET's semantic logging APIs introduced in version 1.5.56, enabling richer structured logging capabilities.

New Features:

• Semantic Logging: Serilog now receives message templates with named and positional parameters for true structured logging
• Enhanced Template Support: Full support for Serilog destructuring (@), stringification ($), and format specifiers (e.g., :N2)
• ForContext Integration: Semantic logging works seamlessly with ForContext() for enriched log contexts
• Akka Metadata Preservation: All Akka.NET metadata (timestamp, log level, thread, logger name) is preserved in structured logs
• Backwards Compatible: Fully compatible with older Akka.NET versions through LogMessage type checking