[Bug](agg-state) fix agg state inner type not conversioned

[BiteTheDDDDt]

What problem does this PR solve?

drop table if exists t01;
create table t01(id int, decimal_col agg_state<sum(decimal(20,6))> generic) properties ("replication_num" = "1");
insert into t01 values (1, sum_state(10.1)), (1, sum_state(20.1)), (2, sum_state(10.2)), (2, sum_state(11.0));
select sum_merge(decimal_col) from t01 group by id;

[18:36]MySQL root@172.20.48.119:test_agg_state> select sum_merge(decimal_col) from t01 group by id; (1105, "errCode = 2, detailMessage = (172.20.48.119)[INTERNAL_ERROR]AggState(function_name=sum,result_is_nullable=true,arguments=[Nullable(Decimal(27, 9))],be_exec_version=8)'s expect return type is Nullable(Decimal(27, 9)), but input Nullable(Decimal(76, 6))") [18:36]MySQL root@172.20.48.119:test_agg_state>

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[BiteTheDDDDt]

run buildall

[hello-stephen]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
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4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[BiteTheDDDDt]

run buildall

[BiteTheDDDDt]

run buildall

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PR approved by anyone and no changes requested.