[Refactoring] Simplify the internal block struture for analog blocks

[jpmoutinho]

Currently there are a lot of definitions in the internal structure of the analog blocks.

The most user facing are defined as python functions that return an instance of a class:

• AnalogRX, AnalogRY, AnalogRZ for a specific axis rotation
• AnalogRot which is the general version of the above with control over all Hamiltonian parameters
• AnalogInteraction which free-evolves the intercation term

The functions above return an instance of:

• ConstantAnalogRotation
• InteractionBlock

And then these classes have an actual implementation in the backends, where for pyqtorch they get converted into an instane of HamEvo, and for Pulser they get translated into a pulse sequence.

To simplify, we could simply have the user-facing operations themselves be defined as classes and possibly get rid of the "intermediate" blocks.

Relevant issues to keep in mind:

• https://github.com/pasqal-io/qadence/issues/192 - a different proposal that could potentially get rid of AnalogRX, AnalogRY, AnalogRZ (and "global" qubit support), but would be harder to implement.
• https://github.com/pasqal-io/qadence/issues/239 - eigenvalues are required for GPSR, and currently they are not directly available from the ConstantAnalogRotation and InteractionBlock (partially because these accept a "global" qubit support).

[jpmoutinho]

@Roland-djee I came back to this issue and played around with the related MR. I am unsure if it should be pursued. It's a huge amount of work to do the complete refactoring, and I think we already have the necessary knowledge on how to properly design a similar feature in the new block system that will avoid all the spaghetti in the current analog blocks.

[RolandMacDoland]

@Roland-djee I came back to this issue and played around with the related MR. I am unsure if it should be pursued. It's a huge amount of work to do the complete refactoring, and I think we already have the necessary knowledge on how to properly design a similar feature in the new block system that will avoid all the spaghetti in the current analog blocks.

Hey, indeed. I would focus on something currently more pressing if this is going to be solved in the new block system.