OTLP trace exporter include W3C trace flags (bits 0–7) in Span.Flags

[nikhilmantri0902]

Closes #7436

Span.Flags should include:
Bits 0–7: span’s W3C TraceFlags (e.g., sampled)
Bits 8–9: “has parent isRemote” and “parent isRemote” per OTLP spec

Update the trace exporter to include the span’s W3C trace flags in the lower 8 bits and keep the existing 8–9 isRemote logic.
Conceptually:
For spans: flags := uint32(sd.SpanContext().TraceFlags() & 0xff)
Always set SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK
If sd.Parent().IsRemote(), also set SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK
Assign s.Flags = flags
Apply the same for links using the link’s SpanContext.TraceFlags() for bits 0–7 and the link’s SpanContext.IsRemote() for bits 8–9.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.1%. Comparing base (07a26be) to head (d504a2c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7438   +/-   ##
=====================================
  Coverage   86.1%   86.1%           
=====================================
  Files        291     291           
  Lines      25613   25615    +2     
=====================================
+ Hits       22056   22059    +3     
+ Misses      3184    3183    -1     
  Partials     373     373           

Files with missing lines	Coverage Δ
...ers/otlp/otlptrace/internal/tracetransform/span.go	93.2% <100.0%> (+<0.1%)	⬆️

... and 1 file with indirect coverage changes

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[nikhilmantri0902]

@dmathieu can we merge this? Resolving conflicts.

[dmathieu]

We require 2 approvals.

[nikhilmantri0902]

@flc1125 can you take a look please?

[flc1125]

@flc1125 can you take a look please?

Sorry, I was on vacation recently. Just got back and have been quite busy lately. I need some time.