Use hard-coded precision of 12 instead of 4

[vorburger]

@xuhcc how about this?

Or do you have to know how to do this better, and actually use the precision set on a commodity in Beancount? (I do not know how to do that.)

[xuhcc]

I prefer 4 but it can be made configurable via envvar

[vorburger]

I prefer 4 but it can be made configurable via envvar

That actually just feels so "redundant"... when I have a bit more time than I do right now, then I'll try to see if we couldn't just import prices "with the precision used in the JSON"... So, looking e.g. at https://api.frankfurter.dev/v1/latest, it should "automagically" be precision 4 for most of those prices which use 4, but be 1, or 2 or 3 (or 5, for GBP) for some of the others. For BTC from Fixer.io & exchangeratesapi.io it would then "automagically" be 6. Would that make sense to you @xuhcc ?

PS: Alternatively, perhaps it's worth for someonw to poke around more how beanprice itself does it...

[xuhcc]

If I remember correctly, precision of prices affects precision of amounts in various reports. Perhaps numbers provided by API at the time had too much decimal places, so I decided to truncate them.