refactor(meta): some simple style refactors

[xxchan]

What's changed and what's your intention?

1. replace match entry with or_insert
2. remove the dispatch_upstreams parameter, and directly update ctx.dispatches instead.
3. make rewrite submodule of fragmenter because it only add (internal) methods to StreamFragmenter. Then we can remove some pub(super) of StreamFragmenter

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)

[TennyZhuang]

Why closed?

[xxchan]

Because of conflicts with another huge refactor #2040

[xxchan]

Reopen because I found the conflicts are resolvable 🤪

[codecov]

Codecov Report

Merging #2061 (b173f56) into main (f1b7bcf) will increase coverage by 0.00%.
The diff coverage is 12.90%.

@@           Coverage Diff           @@
##             main    #2061   +/-   ##
=======================================
  Coverage   70.86%   70.87%           
=======================================
  Files         633      633           
  Lines       81404    81387   -17     
=======================================
- Hits        57683    57679    -4     
+ Misses      23721    23708   -13     

Flag	Coverage Δ
rust	70.87% <12.90%> (+<0.01%)	⬆️

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% <ø> (ø)
src/meta/src/stream/stream_manager.rs	60.50% <0.00%> (+0.47%)	⬆️
src/meta/src/stream/graph/stream_graph.rs	63.61% <14.28%> (+0.40%)	⬆️
src/meta/src/stream/fragmenter/mod.rs	83.17% <50.00%> (ø)
src/common/src/types/ordered_float.rs	23.70% <0.00%> (+0.19%)	⬆️
.../src/executor/managed_state/aggregation/extreme.rs	90.29% <0.00%> (+0.26%)	⬆️

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