[TEST] Multiple exports in OTLP HTTP exporters tests

[owent]

Fixes #3721

Changes

• Allow retryable exports or split them into two batch jobs for OTLP HTTP exporters.

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

[Copilot]

Pull request overview

This PR modifies OTLP HTTP exporter tests to support multiple export attempts in unit tests, addressing issue #3721. The changes enable tests to handle retryable exports or split batch jobs.

Key Changes

• Changed mock expectations from .WillOnce() to .WillRepeatedly() to allow multiple export invocations
• Added early-return guards to handle empty payloads gracefully
• Introduced counter validation to ensure at least one successful export occurred

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 14 comments.

File	Description
exporters/otlp/test/otlp_http_metric_exporter_test.cc	Updated 6 test methods to support retryable metric exports with counter validation
exporters/otlp/test/otlp_http_log_record_exporter_test.cc	Updated 4 test methods to support retryable log exports with counter validation
exporters/otlp/test/otlp_http_exporter_test.cc	Updated 4 test methods to support retryable trace exports with counter validation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.93%. Comparing base (69e62f7) to head (dde5719).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3771   +/-   ##
=======================================
  Coverage   89.93%   89.93%           
=======================================
  Files         225      225           
  Lines        7165     7165           
=======================================
  Hits         6443     6443           
  Misses        722      722           

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[marcalff]

LGTM, thanks for the fix.