Optimize `WideDecimalBinaryExpr`: skip the null-masking pass in non-ANSI mode when nothing overflows

[andygrove]

Part of #4936.

Problem

WideDecimalBinaryExpr implements wide (128-bit intermediate) decimal + - *, which runs on the hot path of most TPC-DS queries. It computes the result in a single fused try_binary pass (native/spark-expr/src/math_funcs/wide_decimal_binary_expr.rs), writing i128::MAX as an overflow sentinel in non-ANSI mode. It then unconditionally runs null_if_overflow_precision to convert sentinels into nulls:

let result = if eval_mode != EvalMode::Ansi {
    result.null_if_overflow_precision(p_out)
} else {
    result
};

null_if_overflow_precision is a second full pass that allocates a new array, and it runs even when no value overflowed, which is the common case.

Proposed change

Run the masking pass only when a sentinel is actually present, mirroring what was done for DecimalRescaleCheckOverflow in #4938:

let result = if eval_mode != EvalMode::Ansi && result.values().contains(&i128::MAX) {
    result.null_if_overflow_precision(p_out)
} else {
    result
};

contains short-circuits at the first sentinel, so the overflow path is unaffected while the common no-overflow path skips the extra allocation. ANSI mode never produces a sentinel (it errors during the try_binary pass) and is unchanged.

Output stays bit-identical: when no sentinel is present, null_if_overflow_precision would have nulled nothing, so skipping it yields the same array.

Notes

This is the non-ANSI counterpart to the CheckOverflow ANSI fast path in #4937. A review of the other decimal expressions found no remaining ANSI-detection asymmetry: DecimalRescaleCheckOverflow (#4938), WideDecimalBinaryExpr, and the decimal casts already do their ANSI overflow check inside a single cheap pass.

A criterion benchmark (no-overflow, no-overflow-with-nulls, sparse-overflow, dense-overflow, and an ANSI shape) should accompany the change to confirm the win and that overflow shapes do not regress.