Consolidate `FragmentsModel` / `SingleThreadedFragmentsModel` return types

[ShaMan123]

Description 📝

There are methods that do not share the same signature between FragmentsModel / SingleThreadedFragmentsModel.
This is undesirable, making the writing of helper functions accepting a model arg awkward.

export async function hashItemsWithGeometry(
  model: SingleThreadedFragmentsModel | FragmentsModel,
  precision = GEOMETRY_FLOATING_POINT_PRECISION
) {
  const value: number[] | Item[] = await model.getItemsWithGeometry(); // awkward
  await model.getItemsIdsWithGeometry(); // doesn't exist on SingleThreadedFragmentsModel, viable solution if exists
}

Suggested solution 💡

Consolidate signatures so that both classes have an identical (or almost identical) interface (I think SingleThreadedFragmentsModel can remain sync though)

Alternative ⛕

I could use instanceof to differentiate between the 2

Additional context ☝️

No response

Validations ✅

• Read the docs.
• Check that there isn't already an issue that requests the same feature to avoid creating a duplicate.

[ShaMan123]

getItemsVolume doesn't exist in SingleThreadedFragmentsModel

[ShaMan123]

After inspecting the code I think SingleThreadedFragmentsModel should extend VirtualFragmentsModel.
VirtualFragmentsModel methods can change access to protected/private if needed