[EP] Refactor and making it more modular.

[MaoZiming]

Description

Please include a summary of the changes and the related issue.

• remove run_local
• Refactor EFA-specific code paths.
• Remove peer_copy_worker and manager.
• Switch to subset_barrier.

Fixes # (issue)

Type of Change

• Bug fix
• New feature
• Documentation update

How Has This Been Tested?

Include any tests here.

• Unit tests
• Integration tests
• Manual testing

Checklist

• My code follows the style guidelines, e.g. format.sh.
• I have run build_and_install.sh to verify compilation.
• I have removed redundant variables and comments.
• I have updated the documentation.
• I have added tests.