refactor(stream): refine AggExecutor and Executor

[TennyZhuang]

Signed-off-by: TennyZhuang [email protected]

What's changed and what's your intention?

PLEASE DO NOT LEAVE THIS EMPTY !!!

The relation between Executor and AggExecutor are combinations, not inheritance, so no structure should implement them both.

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)

[BugenZhao]

LGTM!

[codecov]

Codecov Report

Merging #1795 (2145601) into main (62aba2a) will increase coverage by 0.00%.
The diff coverage is 39.13%.

@@           Coverage Diff           @@
##             main    #1795   +/-   ##
=======================================
  Coverage   71.22%   71.23%           
=======================================
  Files         605      605           
  Lines       78931    78925    -6     
=======================================
  Hits        56219    56219           
+ Misses      22712    22706    -6     

Flag	Coverage Δ
rust	71.23% <39.13%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
src/stream/src/executor_v2/agg.rs	89.47% <0.00%> (ø)
src/stream/src/executor_v2/hash_agg.rs	94.36% <0.00%> (+0.34%)	⬆️
src/stream/src/executor_v2/global_simple_agg.rs	93.14% <56.25%> (+0.74%)	⬆️
src/stream/src/executor_v2/local_simple_agg.rs	97.67% <100.00%> (+0.90%)	⬆️

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