What problem does this PR solve?

Integer-to-DecimalV3 casts with zero scale previously went through the generic decimal cast path even when the target decimal precision can represent the full integer input range. For example, casting an INT column to DECIMALV3(10, 0) still used the common _from_int helper, which computes decimal scaling and range-related values that are unnecessary when the scale is zero and the cast cannot narrow the integer range.

Root cause: the DecimalV3 cast implementation did not have a direct fast path for non-narrowing integer casts to zero-scale decimal types.

This change adds a direct zero-scale DecimalV3 path for integer and boolean inputs when the target decimal range is not narrower than the input range. The fast path writes the input value directly into the decimal native value and preserves the existing generic path for narrowing casts, non-zero-scale casts, and overflow-sensitive cases.

Local optest profiling for:

select sum(cast(quantity as decimalv3(10,0))) from q14_avg_expr_100m;

showed the cast expression time improving from about 119.0 ms to about 109.7 ms on 100M rows, roughly an 8% reduction in this expression counter.

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

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