Byron Hambly 39e34a608b
fix: fix potential overflow in max_bitcoin_for_price
In testing, ASB panicked in `max_bitcoin_for_price` when the Monero
balance x Bitcoin price was enough to overflow `u64`.

This commit changes the function to do the piconero offset division
first, and then to use `checked_mul` to return None if the calculation
would overflow. This required changing the function return
signature to an `Option`. Additional tests for the function were also added.

MONERO_FEE was changed from 0.000030 to 0.000016, which is still
double the current median transaction fee listed at
https://www.monero.how/monero-transaction-fees as of 2022-07-28.
2022-07-28 15:03:32 +02:00
..