Reverse RH/LH sharding, phrase encoding

- Flips sharding from RH bits to LH bits. Fixes bad clustering of degen and term shards b/c of RH 4bit encoded distance/weights.
- Flips phrase/1st term encoding for phrase index to work with RH/LH sharding switch.
- Refactors cache test to use mem source and skip the hard to use disk fixtures.