[opt](expr) use compiler builtin for int128 multiplication overflow checks

[Mryange]

What problem does this PR solve?

Checked int128 multiplication used a division-based software implementation. On x86-64, this
generated a call to the expensive __udivti3 helper in the decimal multiplication path.

This change uses __builtin_mul_overflow, allowing the compiler to emit inline multiplication and
carry instructions without a runtime helper call. It also adds boundary coverage and 10,000
deterministic random input pairs that validate both the overflow flag and low 128 result bits against
an Int256 oracle.

For the query-like DECIMAL64(10,7) * DECIMAL128(38,2) -> DECIMAL128(38,9) benchmark with 65,536
items per batch, using aggregate CPU mean from five repetitions:

Path	Before	After	Improvement
Production, including precision-38 check	21.32 ns/item	6.32 ns/item	70.34%
Native overflow check only	21.06 ns/item	4.13 ns/item	80.37%

Release note

None

Check List (For Author)

• Test: Manual test
  • Release benchmark build: sh build.sh --benchmark -j48
  • Benchmark correctness validation against Int256 oracle
  • clang-format 16 check
• Behavior changed: No
• Does this need documentation: No

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

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
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?

[Mryange]

run buildall