[SDK] Preserve unlimited batch processor shutdown timeout

[Soundcreates]

Fixes #4681

Changes

• Preserve the default std::chrono::microseconds::max() timeout when batch span and log record processors shut down their exporters.
• Preserve the unlimited timeout when MultiLogRecordProcessor shuts down each child processor.
• Assert that every multi-log child receives the unlimited timeout during default shutdown and that finite shutdowns continue sharing the remaining timeout budget.
• Add the fix to the unreleased changelog with the PR link.

Testing

• Built multi_log_record_processor_test, batch_log_record_processor_test, and batch_span_processor_test with CMake and GCC 13.3.
• multi_log_record_processor_test: 7 passed.
• batch_log_record_processor_test: 13 passed.
• batch_span_processor_test: 12 passed.
• Ran clang-format 18 on the changed C++ file.
• Ran git diff --check.
• Ran markdownlint on CHANGELOG.md.
• Full platform and build-system coverage is left to CI.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed. There is no public API change.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-09T11:48:27.580242Z	b04a6ae	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: b04a6ae5ab

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• Open a pull request for review
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.77%. Comparing base (91bef1e) to head (090e10f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4686      +/-   ##
==========================================
- Coverage   86.83%   86.77%   -0.05%     
==========================================
  Files         525      525              
  Lines       20741    20747       +6     
==========================================
- Hits        18008    18002       -6     
- Misses       2733     2745      +12     

Files with missing lines	Coverage Δ
sdk/src/logs/batch_log_record_processor.cc	91.10% <100.00%> (-3.11%)	⬇️
sdk/src/logs/multi_log_record_processor.cc	96.60% <100.00%> (+0.13%)	⬆️
sdk/src/trace/batch_span_processor.cc	88.89% <100.00%> (-3.28%)	⬇️

... and 1 file with indirect coverage changes

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[dbarker]

Thanks for the fix. Please see feedback below.

[Soundcreates]

I have addressed all the feedback comments, please review whenever you get a chance.

[dbarker]

Thanks for the fix.