nonnative arithmetic doesn't support < 3 limbs configuration

[slumber]

The following code panics if you attempt to use configuration with 1 or 2 limbs

r1cs-std/src/fields/nonnative/reduce.rs

Lines 170 to 174 in 2ca3bd7

	if 2 * params.bits_per_limb + ark_std::log2(params.num_limbs) as usize
	> BaseField::MODULUS_BIT_SIZE as usize - 1
	{
	panic!("The current limb parameters do not support multiplication.");
	}

However, I don't remember bellman-bignat having this limitation

r1cs-std/src/fields/nonnative/reduce.rs

Line 276 in 2ca3bd7

// The following code is adapted from https://github.com/alex-ozdemir/bellman-bignat/blob/master/src/mp/bignat.rs#L567

This could be a problem if nonnative params become configurable