converterrunner: Do not round values unnecassarily

We pass in the precision when we format the string
and the rounding causes internal issues when the value is casted to an
int.

Test Plan:
Large queries like `100000000000000000000000000000000000000000$` no
longer produce negative results.

CCBUG: 425790

This fix can also be backported for Plasma 5.21.