refactor(streaming): move agg mod to executor v2

[pleiadesian]

What's changed and what's your intention?

As title. Also, AggExecutorWrapper is moved into agg mod.

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 #1885 (7e06634) into main (ebdb341) will increase coverage by 0.01%.
The diff coverage is 96.36%.

@@            Coverage Diff             @@
##             main    #1885      +/-   ##
==========================================
+ Coverage   70.70%   70.72%   +0.01%     
==========================================
  Files         611      610       -1     
  Lines       79861    79844      -17     
==========================================
+ Hits        56465    56466       +1     
+ Misses      23396    23378      -18     

Flag	Coverage Δ
rust	70.72% <96.36%> (+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/global_simple_agg.rs	0.00% <ø> (ø)
src/stream/src/executor/hash_agg.rs	0.00% <ø> (ø)
src/stream/src/executor/integration_tests.rs	95.70% <ø> (ø)
src/stream/src/executor/local_simple_agg.rs	0.00% <ø> (ø)
.../src/executor/managed_state/aggregation/extreme.rs	90.00% <ø> (-0.27%)	⬇️
...ream/src/executor/managed_state/aggregation/mod.rs	79.45% <ø> (ø)
...am/src/executor/managed_state/aggregation/value.rs	96.42% <ø> (ø)
src/stream/src/executor/mod.rs	51.51% <ø> (ø)
src/stream/src/executor_v2/aggregation/agg_call.rs	87.50% <ø> (ø)
src/stream/src/executor_v2/aggregation/foldable.rs	88.10% <ø> (ø)
... and 14 more

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