pdg_sig_figs value rounding issue with zero or non-finite uncertainty

[jagerber48]

from sciform import Formatter, FormatOptions
sform = Formatter(FormatOptions(pdg_sig_figs=True))
print(sform(123, 0))

erroneously results in '120 +/- 0'. The value is erroneously rounded according to pdg sig fig rules, but these rules should only apply t the uncertainty. In this case, the value should be rounded according to the AutoDigits rules.

[jagerber48]

closed by #67