refactor: rename flow task to flow

[WenyXu]

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Refer to a related PR or issue link (optional)

#3664

What's changed and what's your intention?

Wait for #3810
Remove all task suffix.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[codecov]

Codecov Report

Attention: Patch coverage is 56.56168% with 331 lines in your changes are missing coverage. Please review.

Project coverage is 85.32%. Comparing base (b493ea1) to head (b2b0073).

❗ Current head b2b0073 differs from pull request most recent head dec1360. Consider uploading reports for the commit dec1360 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3833      +/-   ##
==========================================
- Coverage   85.60%   85.32%   -0.28%     
==========================================
  Files         954      954              
  Lines      163072   163038      -34     
==========================================
- Hits       139601   139116     -485     
- Misses      23471    23922     +451