fix: decimal conversion

[ntheile]

Fix decimal conversion function and adds support for 3 decimal currencies.

[testerez]

Do we really need moneyphp? Converting to smallest unit is pretty simple without any external library. Here is an example, copied from zaprite-v2 and ported to PHP:

<?php

function get_currency_smallest_unit_factor($currency) {
    // source: https://stripe.com/docs/currencies
    if (in_array($currency, ['CLP','JPY','KRW','UGX','VND'])) return 1;
    if (in_array($currency, ['BHD','JOD','KWD','OMR','TND'])) return 1000;
    if (in_array($currency, ['BTC', 'LBTC'])) return 100_000_000;
    return 100;
}

function to_smallest_unit($amount, $currency) {
    return round($amount * get_currency_smallest_unit_factor($currency));
}

function from_smallest_unit($amount, $currency) {
    return $amount / get_currency_smallest_unit_factor($currency);
}

For info, I realised zaprite-v2 was not handling 3 decimal currencies correctly. Fixed here: https://github.com/ZapriteApp/zaprite-v2/pull/1336