Youpin Doppler ask prices

Youpin ask prices now cover Doppler and Gamma Doppler variants. Phase 1 through Phase 4, Ruby, Sapphire, Black Pearl, and Emerald each carry independent prices, refreshed every ~15 minutes.

The per-phase prices are returned in the variants object on GET /v1/prices/latest and POST /v1/prices/history, keyed by version.