improve number.AsRatio() conversion using stellar/go/price for more accurate pricing on centralized exchanges

[nikhilsaraf]

Describe the bug

The bot does not accurately handle prices for centralized exchanges

Expected behavior

I think the bot should correctly convert prices for centralized exchanges even though it leans on a 32-bit N/D conversion process for Price.

Frequency

The frequency is: Always susceptible to incorrect conversions, especially for finer grained float values

Possible Solution

This bug can be fixed by using the inbuilt price.Parse(v string) converter for the stellar library at github.com/stellar/go/price.

see commit in https://github.com/nikhilsaraf/kelp/tree/improve_number_as_ratio