Group and Mineral IDs - Integers vs Objects

[morganjwilliams]

When incorporating mineral and group names from TSG outputs, these could be alternately stored as integers/IDs which point to a mapping (efficient for storage), or strings/objects (where a mapping is retained principally for back-compatibility/traceability). Currently this is mixed between mineral and group names, and perhaps should be standardised - either with an option during reading, or simply taking e.g. the latter option by default.

Given that common export formats (i.e., Zarr) would likely handle some of the compression aspects, storing strings for user-friendliness might make sense.