feat(meta): let stream actors in fragment share same stream node

[wenym1]

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What's changed and what's your intention?

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

• My PR needs documentation updates.

Release note

[wenym1]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(meta): let stream actors in fragment share same stream node #20310 👈 (View in Graphite)
• refactor(meta): do not store upstream actors in merge node #20222
• main

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[gru-agent]

This pull request has been modified. If you want me to regenerate unit test for any of the files related, please find the file in "Files Changed" tab and add a comment @gru-agent. (The github "Comment on this file" feature is in the upper right corner of each file in "Files Changed" tab.)