Removes redundant initializers from the constructor and provides
initializers for all members that don't already have one for consistency
(and deterministic initial state).
Given the volume verifier has quite a few non-trivial object within it,
it's best to default the destructor within the cpp file to prevent
inlining complex destruction logic elsewhere, while also making it nicer
if a forward-declared type is ever used in a member variable.
Lioncash