feat: separate handling for sum aggregation function of Int256.

[shanicky]

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What's changed and what's your intention?

This PR implements a separate, rough sum function for non-primitive types such as Int256. This should be considered and removed during future refactoring of the aggregation functions.

Checklist For Contributors

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
  - [ ] I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features Sqlsmith: Sql feature generation #7934).
• I have demonstrated that backward compatibility is not broken by breaking changes and created issues to track deprecated features to be removed in the future. (Please refer to the issue)
• All checks passed in ./risedev check (or alias, ./risedev c)

Checklist For Reviewers

• I have requested macro/micro-benchmarks as this PR can affect performance substantially, and the results are shown.

Documentation

Click here for Documentation

Types of user-facing changes

Please keep the types that apply to your changes, and remove the others.

• SQL commands, functions, and operators

Release note

[codecov]

Codecov Report

Merging #9191 (d481982) into main (77aacbd) will increase coverage by 0.00%.
The diff coverage is 86.27%.

@@           Coverage Diff            @@
##             main    #9191    +/-   ##
========================================
  Coverage   70.82%   70.82%            
========================================
  Files        1200     1201     +1     
  Lines      200261   200363   +102     
========================================
+ Hits       141829   141902    +73     
- Misses      58432    58461    +29     

Flag	Coverage Δ
rust	70.82% <86.27%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
src/expr/src/sig/agg.rs	19.04% <0.00%> (-0.19%)	⬇️
src/expr/src/vector_op/agg/aggregator.rs	55.13% <66.66%> (+0.19%)	⬆️
src/expr/src/vector_op/agg/non_primitive_sum.rs	87.75% <87.75%> (ø)

... and 9 files with indirect coverage changes

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[wangrunji0408]

LGTM