ArithmeticValue always reports a nullable result type, even when both operands are not nullable

[g31pranjal]

Noticed while reviewing #4617.

The problem

ArithmeticValue.getResultType() derives only the type code from the physical operator and takes the default nullability:

// ArithmeticValue.java
@Override
public Type getResultType() {
    return Type.primitiveType(operator.getResultTypeCode());
}

and the single-argument overload is nullable:

// Type.java
static Type primitiveType(@Nonnull final TypeCode typeCode) {
    return primitiveType(typeCode, true);
}

So a + b is typed nullable even when a and b are both not-nullable. Arithmetic on not-null operands cannot produce null, so this loses information for every arithmetic expression in the system.

Where it bites

In LogicalOperator.generateCorrelatedFieldAccess, the SQL AT ordinal is built as explodeOrdinal + 1, where the ordinal is a field of the explode result typed Type.primitiveType(INT, false) and the literal comes from LiteralValue.ofScalar(1), which is Type.fromObject(1) = Type.primitiveType(INT, false). Both operands are not-nullable, yet the sum is nullable, while the column is declared with DataType.Primitives.INTEGER.type(), i.e. IntegerType.notNullable(). The declared SQL type and the underlying value type therefore disagree.