feat(flow): add eval_batch for ScalarExpr

[discord9]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

What's changed and what's your intention?

add eval_batch for flow's ScalarExpr, which can be use later to optimize performance for flow and reduce small object alloc/dealloc(which is found to be a very large cost on cpu time when profiling flow tasks).

The major change of logic happens in the following files:

• src/flow/src/expr/func.rs include three eval_batch function
• src/flow/src/expr/scalar.rs 's ScalarExpr::eval_batch function
• src/flow/src/expr/df_func.rs's eval_batch function

and other changes are just moving file around and remove unused imports

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.

[coderabbitai]

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[codecov]

Codecov Report

Attention: Patch coverage is 26.80180% with 325 lines in your changes missing coverage. Please review.

Project coverage is 84.50%. Comparing base (5aa4c70) to head (80a27b1).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4551      +/-   ##
==========================================
- Coverage   84.94%   84.50%   -0.44%     
==========================================
  Files        1090     1093       +3     
  Lines      194325   195994    +1669     
==========================================
+ Hits       165069   165625     +556     
- Misses      29256    30369    +1113     

[fengjiachun]

@discord9 Good job, could you show us the performance analysis comparison before and after this PR to clearly see the optimization effect?

[discord9]

@discord9 Good job, could you show us the performance analysis comparison before and after this PR to clearly see the optimization effect?

It would still require some more change of code to make MapFilterProject Operator to use batching process, which I'm working on adding it, will include performance analysis in later PR

[fengjiachun]

error: unused import: `common_telemetry::debug`
  --> src/flow/src/expr/func.rs:22:5
   |
22 | use common_telemetry::debug;
   |     ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `-D unused-imports` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(unused_imports)]`

CI failed, cc @discord9

[fengjiachun]

LGTM