default initialize particles?

[nicolasaunai]

Should we allow for default particle init? I don't think so unless it's so much trouble not to.

[PhilipDeegan]

we have a case where we do actually use a default initialized particle for diagnostics. I believe it's in order to forward the type to highfive to create a dataset, and the values are not "used" per se

other than that there some default initialized particles in tests

the simplest approach might be multiple classes, where the current "Particle" class becomes non-default construcbile, but it inherits from a super class "AParticle(?)" which is default constructible

or the particle class has an optional template param deciding if it's default constructible