Span Exporter async native

[lalitb]

Changes

TODO - changelog

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 63 lines in your changes missing coverage. Please review.

Project coverage is 79.1%. Comparing base (ac69af6) to head (7086a66).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-otlp/src/exporter/http/trace.rs	0.0%	20 Missing ⚠️
opentelemetry-otlp/src/span.rs	0.0%	18 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/trace.rs	0.0%	12 Missing ⚠️
...sdk/src/trace/span_processor_with_async_runtime.rs	82.6%	4 Missing ⚠️
opentelemetry-stdout/src/trace/exporter.rs	0.0%	3 Missing ⚠️
opentelemetry-sdk/src/trace/runtime_tests.rs	0.0%	2 Missing ⚠️
opentelemetry-zipkin/src/exporter/mod.rs	0.0%	2 Missing ⚠️
opentelemetry-otlp/src/exporter/http/mod.rs	0.0%	1 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/mod.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2685   +/-   ##
=====================================
  Coverage   79.1%   79.1%           
=====================================
  Files        122     122           
  Lines      22543   22530   -13     
=====================================
- Hits       17850   17843    -7     
+ Misses      4693    4687    -6     

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[cijothomas]

LGTM! Can you add a changelog entry for the breaking change in export traits