Eliminate/mitigate overflow (and rounding)

It seems you always need to specify how many decimals, e.g. with FixedDecimal{Int8, 2} and that type which is far from optional. Most likely it's not useful enough for money, and when you want to base on Int8 otherwise likely binary fixed point better.

I suggest as a happy medium for your docs, instead of (or have both):
>For example, FixedDecimal{Int8, 2} allows you [to a] decimal number with up to 2 fractional digits.

const FixedSafeDecimal = FixedDecimal{Int32, 3}

I intentionally didn't go with Int64, since then you multiply two such numbers you could get FixedDecimal{Int64, 6} and you don't need to check for overflows nor round, and I would like that type to do it by default. It's just an idea for your package, I've been thinking of making my own, and I could do that and wrap yours, in case you don't want to implement this.

You can add and subtract, and then there is a possibility of one extra bit, this overflow, in case you want to check for that, or just go to FixedDecimal{Int64, 3}, note not there ,6. The division is the problem, then I would argue for going to a rational rather than Float64 or either these types.

Because in that case and at least for multiplying you want to put the "genie-back-into-the bottle", and I suggest a round back to FixedSafeDecimal with overflow check postponed until then.