feat: add semantic logging support for Akka.NET 1.5.56+

[Aaronontheweb]

Summary

Adds semantic logging support to leverage Akka.NET's new semantic logging APIs introduced in version 1.5.56.

This major enhancement enables Microsoft.Extensions.Logging (MEL) to receive properly structured state dictionaries instead of pre-formatted strings, unlocking the full power of structured logging for all MEL sinks (Serilog, Seq, Application Insights, etc.).

Changes

• LoggerFactoryLogger.cs: Completely rewrote Log() method to extract structured properties and create MEL state dictionary
• SemanticLoggingSpecs.cs: Added comprehensive test suite with 7 tests covering all semantic logging scenarios

Test Coverage

New test suite includes:

• Named and positional template properties
• Multiple properties handling
• Akka metadata preservation (ActorPath, Timestamp, Thread, LogSource)
• OriginalFormat key verification (MEL convention)
• Format specifiers handling
• Empty properties handling

All existing tests pass (457/458, 1 skipped - same as before).

Impact

This change enables MEL sinks to:

• Query log entries by structured property values
• Correlate events across distributed systems
• Create rich dashboard visualizations
• Perform advanced filtering and analysis

Example State Dictionary

Before: MEL received formatted string "User 12345 with email user@example.com logged in"

After: MEL receives structured state:

{
  "UserId": 12345,
  "Email": "user@example.com",
  "ActorPath": "akka://sys/user/myactor",
  "Timestamp": <DateTime>,
  "Thread": 17,
  "LogSource": "MyActor",
  "OriginalFormat": "User UserId with email Email logged in"
}

Backwards Compatibility

Fully backwards compatible through conditional TryGetProperties() check. Falls back to ToString() for non-structured messages.

Dependencies

Requires Akka.NET >= 1.5.56 (not yet released)

Notes

• CI/CD will fail until Akka.NET 1.5.56 is published to NuGet
• This PR is ready for review but should not be merged until the Akka.NET dependency is available