Support casting negative scale decimals to numeric

[Chiicake]

Which issue does this PR close?

• Closes Support casting negative scale decimals to numeric #9201 .

Rationale for this change

Casting decimals with negative scale to integer types currently errors because the scale factor is always applied as a division. Negative scales represent powers of ten that should scale the integer value up, so the cast should multiply instead.

What changes are included in this PR?

• Apply the scale factor using multiplication when scale < 0 in cast_decimal_to_integer.

Are these changes tested?

Yes, the test given by issue is passed.

// arrow-cast/src/cast/mod.rs
    #[test]
    fn test_cast_decimal_to_numeric_negative_scale() {
        let value_array: Vec<Option<i256>> = vec![
            Some(i256::from_i128(125)),
            Some(i256::from_i128(225)),
            Some(i256::from_i128(325)),
            None,
            Some(i256::from_i128(525)),
        ];
        let array = create_decimal256_array(value_array, 38, -1).unwrap();

        generate_cast_test_case!(
            &array,
            Int64Array,
            &DataType::Int64,
            vec![Some(1_250), Some(2_250), Some(3_250), None, Some(5_250)]
        );
    }

Are there any user-facing changes?

No.