## Description
Previously, the notional cache was using the `float64` type to manipulate price data. Since floating point types can't represent price data accurately, this commit changes the codebase to use a lossless representation (i.e.: `decimal.Decimal`).
### Summary
Tracking issue: https://github.com/wormhole-foundation/wormhole-explorer/issues/344
Before this pull request, there were two separate token databases (one being used by the InfluxDB backfiller, and another one in the `common/` module being used by the analytics service).
Having two different token databases resulted in inconsistencies, due to each of these databases containing different tokens.
This PR unifies those two databases into a single one, under the `common/` module.
agodnic