fix: bn overflow error

[ZhengYuTay]

most of the time calling toNumber() would result in Number can only safely store up to 53 bits, workaround is to just call toString() into Number()

[thaaddeus]

I've seen it as well, would be great to have it fixed in the lib directly, could be someone setting orders with very large prices that causes that? not sure.

[ZhengYuTay]

@armaniferrante, can help take a look with this? Some serum orderbook break when fetching l2 because of large number, this would mitigate it

[thaaddeus]

@ZhengYuTay I think this fix is incorrect in away not preserving decimal places, I think https://github.com/MikeMcl/big.js/ should be used instead for making division?
@armaniferrante I think order ids like 340282366920938463463374607431743501208 for example can trigger this issue.