refactor(fragmenter): split fileds into different structs -- lose weight!

[xxchan]

What's changed and what's your intention?

• Mutable states are split into BuildFragmentGraphState and BuildActorGraphState

  The two stage of fragmenter is orthogonal, after splitting the mutable states into two places, what variables are mutated/referenced become more clear, and only &self is used for StreamFragmenter

• For the remaining fields, XxManagerRef can be used directly thus removed. parallel_degree and is_legacy_frontend are kept for simplicity

Checklist

• [ ] I have written necessary docs and comments
• [ ] I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #2074 (84aa937) into main (1d90e34) will decrease coverage by 0.01%.
The diff coverage is 64.89%.

@@            Coverage Diff             @@
##             main    #2074      +/-   ##
==========================================
- Coverage   70.82%   70.81%   -0.02%     
==========================================
  Files         633      633              
  Lines       81374    81416      +42     
==========================================
+ Hits        57637    57658      +21     
- Misses      23737    23758      +21     

Flag	Coverage Δ
rust	70.81% <64.89%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
...c/meta/src/stream/fragmenter/rewrite/delta_join.rs	0.00% <0.00%> (ø)
src/meta/src/stream/fragmenter/mod.rs	84.13% <90.90%> (+0.95%)	⬆️
...meta/src/stream/fragmenter/graph/fragment_graph.rs	97.14% <100.00%> (-0.14%)	⬇️
...c/meta/src/stream/fragmenter/graph/stream_graph.rs	64.04% <100.00%> (ø)
src/cmd/src/bin/frontend_node.rs	0.00% <0.00%> (-16.67%)	⬇️

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[skyzh]

😋😋😋