consider implementing units in raw_data

[sebkopf]

raw data could be cast as double_with_units, the same way the vendor data table is.

pros:

• convenient for interacting with the data, less cluttered data access, can manage units and scaling independently of column names
• current vs. voltage measurements would probably be fine thanks to the v44 and i44 prefixes

cons:

• unclear how to reconcile raw data between different vendor data types if the units don't match (e.g. if have v44 in mV for one and v44 in V for another) - forced scaling first before aggregation?
• several other processing pipelines already use the implicit unit columns from the raw data and would require fixing by calling an iso_make_units_implicit(prefix = ".", suffix = "") to continue working as used

please chime in if you feel strongly about this possibility