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

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:

```rust
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:

```rust
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.