EmuFreeBackendV2 does not return a pulser.Backend.Results

[a-corni]

Users of EmuFreeBackendV2 (using QutipBackendV2) and EmuMPSBackend (using EmuMPS) expect a pulser.backend.Results from a run. pulser.backend.Results support serialization. This is currently being used in jobs submitted to the cloud via EmuMPSBackend: when the job is finished, job.full_result contains a serialized_result field.

This field is currently missing in jobs submitted to the cloud via EmuFreeBackendV2. Only "raw" and "counter" fields are defined in job.full_result. This is an issue if the users are asking for other observables to be measured than BitString, since the outcome will not be returned.

Solution:

• The MR Fixes: Measuring basis of sequence built with job's variables + deserializing results #220 contains a fix that enables to return pulser.backend.Results if job.full_result contains a serialized_result: This currently enables users to get a pulser.backend.Results if submitting to EmuMPSBackend, but not to EmuFreeBackendV2.
• On the cloud side, associate with the key serialized_result in the data of a results of a job having run on QutipBackendV2, the result of the emulation in its serialized format (with to_abstract_repr).

[a-corni]

@a-quelle-pasqal