fix(sdk-node): support headers_list for log exporters

[LarryHu0217]

Fixes #6953

Changes

• parse declarative headers_list values using the existing percent-decoding key/value parser
• merge explicit headers over headers_list, preserving the documented precedence
• apply the merged values to HTTP headers and gRPC metadata for log exporters
• mark headers_list as handled during exporter creation

Testing

• focused sdk-node create-from-config and utils tests: 93 passing
• sdk-node ESLint
• strict no-emit TypeScript check for the touched header utility
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.07%. Comparing base (636e27a) to head (55c168c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6955   +/-   ##
=======================================
  Coverage   95.07%   95.07%           
=======================================
  Files         409      409           
  Lines       14256    14256           
  Branches     3267     3267           
=======================================
  Hits        13554    13554           
  Misses        702      702           

Files with missing lines	Coverage Δ
...s/opentelemetry-sdk-node/src/create-from-config.ts	95.42% <ø> (ø)
...ental/packages/opentelemetry-sdk-node/src/utils.ts	97.20% <100.00%> (ø)

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Waiting on reviewers · refreshed 2026-07-30 13:48 UTC

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