Replace CorrelationId and CausationId with TraceParent

[toizo]

This PR refactors message metadata handling by removing legacy correlationId and causationId fields and replacing them with OpenTelemetry-compatible Trace Context propagation, as discussed in #101 .

The main changes include:

• Message Metadata:

  • Removed CorrelationId and CausationId from MessageEnvelopeProperties, Metadata, and MessageHandlerContext.
  • Added a TraceParent property to support distributed tracing.

• Tests:

  • Updated or removed tests that referenced correlationId and causationId.
  • Adjusted payloads and assertions to use traceparent instead.

This update aligns Dafda's message tracing with modern distributed tracing standards and simplifies the metadata model.

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