[Feature request]: Refactor MaterialsProjectDataset to not serialize pymatgen Structures in LMDB

[laserkelvin]

Feature/behavior summary

Currently, the workflow implemented for MaterialsProjectDataset will save and reload a pymatgen.Structure object. The issue with this is that it is very intimately tied to the version of pymatgen, where small API changes can make it difficult to reload the dataset in later versions.

Request attributes

• Would this be a refactor of existing code?
• Does this proposal require new package dependencies?
• Would this change break backwards compatibility?
• Does this proposal include a new model?
• Does this proposal include a new dataset?
• Does this proposal include a new task/workflow?

Related issues

No response

Solution description

If we can refactor it so that Structures are created at load time - in line with other dataset implementations - it would make it break this dependency...breaking.

We would have to re-process the existing LMDBs being distributed, and make sure that the data is stored as just plain coordinates, atoms, and lattice parameters.

Additional notes

No response