[pf-evals] Use async batch run for evaluators by default and composite evaluator perf optimization

[ninghu]

Description

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All Promptflow Contribution checklist:

• [ ] The pull request does not introduce [breaking changes].
• [ ] CHANGELOG is updated for new features, bug fixes or other significant changes.
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Testing Guidelines

• [ ] Pull request includes test coverage for the included changes.

[github-actions[bot]]

promptflow-evals test result

 12 files   12 suites   1h 38m 44s :stopwatch:  13 tests  12 :white_check_mark:  1 :zzz: 0 :x: 156 runs  144 :white_check_mark: 12 :zzz: 0 :x:

Results for commit f4ee1f07.

:recycle: This comment has been updated with latest results.