fix petabyte-precision

[lucajackal85]

I cloned your repo and I found that unittest was not running properly on my local environment with php 7.4

After some research I found that the function bcpow has changed in behaviour in php versione 7.3 (see changelog here)

bcpow() now returns numbers with the requested scale. Formerly, the returned numbers may have omitted trailing decimal zeroes.

PHP >= 7.3

var_dump(bcpow(1024,5,10)); 
//string(27) "1125899906842624.0000000000"

var_dump(1 * bcpow(1024,5,10)); 
//float(1.1258999068426E+15)

PHP <7.3

var_dump(bcpow(1024,5,10));
//string(16) "1125899906842624"

var_dump(1 * bcpow(1024,5,10));
//int(1125899906842624)

I've tested the fix with php 7.4 and php 8.0