feat: NeutronSQNode unit tests

[trisyoungs]

Based on #2300 - do not merge until #2300 is resolved

This PR adds unit tests for the NeutronSQNode. One relatively significant change is the way that we now must handle our lists of exchangeable atom types. Previously this was defined as a very literal vector of AtomType* but here the preference is to move to a simple list of atom type names. The reason for that is that multiple species may contain atom types of the same name while not explicitly sharing data through the pointer - a name will capture all such occurrences of a given atom type. This may of course be subject to change as we move forward!

[rprospero]

One optional, stylistic suggestion, but otherwise looks good

[rprospero]

Suggested change

	template <typename Range, typename Lambda> static SerialisedValue fromRange(const Range &range, Lambda toSerial)
	{
	SerialisedValue result = SerialisedValue::array_type{};
	std::transform(range.begin(), range.end(), std::back_inserter(result), toSerial);
	return result;
	}
	template <std::ranges::input_range Range, typename Lambda> static SerialisedValue fromRange(const Range &range, Lambda toSerial)
	{
	SerialisedValue result = SerialisedValue::array_type{};
	std::ranges::copy(std::ranges::views::transform(range, toSerial), std::back_inserter(result));
	return result;
	}

A couple of small changes:

1. Specify that the Range template type must satisfy the input_range concept, which helps narrow down template errors.
2. Use range based transform and copy (mostly to avoid explicit begin and end

This suggestion is entirely optional.