Upgrade Datadog tracer to dd-trace-go v2

[yarinzirlin]

• Updated imports from v1 (gopkg.in/DataDog/dd-trace-go.v1) to v2 (github.com/DataDog/dd-trace-go/v2)
• Updated struct types to use pointers (*tracer.Span, *tracer.SpanContext) as required by v2
• Replaced deprecated ChildOf() pattern with modern v2 approach:
  • Use Span.StartChild() for direct parent spans
  • Use tracer.WithStartSpanConfig() for span contexts
• Updated tests to handle v2 API changes (pointer types for mocktracer.Span)
• Removed unused helper functions (newSpanContextReader, spanContextReader)
• All tests passing

This upgrade ensures compatibility with the latest Datadog APM features and removes dependency on deprecated v1 APIs.

What was changed

Updated dd-trace-go from the deprecated v1 to v2

Why?

1. dd-trace-go v1 stopped working

Checklist

1. How was this tested:
   I ran the upgraded interceptor against my Datadog instance and saw the expected traces

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