Don't rely on jsanitize in Atoms <--> Structure object interconversion

[Andrew-S-Rosen]

Closes #3358.

As raised in #3270, I stated:

Currently, we have the mapping: Atoms.info <--> Structure.properties, since they serve the same purpose between ASE and Pymtatgen, respectively. However, I jsanitize-d the atoms.info before assigning it to .properties to ensure the Structure/Molecule object can be (de)serialized since this is often an implicit assumption of Structure/Molecule objects but is not necessarily one for ASE Atoms objects. In practice, this means that there could be some scenarios where a user interconverts between ASE Atoms and Pymatgen Structure/Molecule with some loss of information; namely, if the atoms.info is modified by jsanitize() then it can't be restored in its original form. There might be a better solution than this, but I implemented it because oftentimes ASE will dump un-serializable class objects (namely, a Spacegroup class) into atoms.info, such as when reading in a CIF with symmetry flags.

I now have avoided the needed to call jsanitize so that we don't lose any info between interconversion. To do this, I have "manually" JSON-ified and reconstructed the ASE Spacegroup object if present. I also did a much-needed general cleanup of both the class and test suite.

[Andrew-S-Rosen]

@chiang-yuan, @janosh: This is ready for your review.

[chiang-yuan]

Just want to offer thanks for this! @Andrew-S-Rosen you are so swift on this! (even on PTO 🫡

[Andrew-S-Rosen]

Had a spare moment and couldn't get it off my mind. I can go back to the beach life now. 😎🏖️