refactor(meta): separate stream graph building into modules & add unit tests for scheduler

[BugenZhao]

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What's changed and what's your intention?

There are no substantial changes except for the unit test for the new scheduler.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

• Close meta: refactor graph building and scheduling #7420
• feat(meta): iterative streaming scheduler (part 2) #7659

[BugenZhao]

Here're the unit tests.

[codecov]

Codecov Report

Merging #7807 (dd65324) into main (42f37b5) will increase coverage by 0.00%.
The diff coverage is 78.59%.

@@           Coverage Diff            @@
##             main    #7807    +/-   ##
========================================
  Coverage   71.68%   71.69%            
========================================
  Files        1103     1105     +2     
  Lines      176072   176180   +108     
========================================
+ Hits       126211   126306    +95     
- Misses      49861    49874    +13     

Flag	Coverage Δ
rust	71.69% <78.59%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/meta/src/stream/test_fragmenter.rs	99.33% <ø> (ø)
src/meta/src/stream/stream_graph/visit.rs	58.09% <58.09%> (ø)
src/meta/src/stream/stream_graph/actor.rs	75.89% <75.89%> (ø)
src/meta/src/stream/stream_graph/fragment.rs	80.55% <80.55%> (ø)
src/meta/src/stream/stream_graph/id.rs	83.33% <83.33%> (ø)
src/meta/src/stream/stream_graph/schedule.rs	92.83% <100.00%> (+5.19%)	⬆️
src/batch/src/executor/group_top_n.rs	68.23% <0.00%> (-6.48%)	⬇️
src/meta/src/hummock/mock_hummock_meta_client.rs	63.45% <0.00%> (-1.02%)	⬇️
src/object_store/src/object/mod.rs	51.30% <0.00%> (-0.22%)	⬇️
src/common/src/types/ordered_float.rs	30.87% <0.00%> (-0.20%)	⬇️
... and 3 more

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[yezizp2012]

LGTM!

[mergify]

Hey @BugenZhao, this pull request failed to merge and has been dequeued from the merge train. If you believe your PR failed in the merge train because of a flaky test, requeue it by clicking "Update branch" or pushing an empty commit with git commit --allow-empty -m "rerun" && git push.