intcomma() loses digits from large decimal strings #496

intcomma() silently loses a fractional digit when given a large decimal string, even with ndigits omitted. The equivalent Decimal input preserves it.

Reproduced on current main (6b817b963dbb091b9ad20a746cb6a26653a93b95; 42 commits after 4.16.0) with Python 3.14.8 on Windows:

from decimal import Decimal
from humanize import intcomma

print(intcomma('1234.12'))
print(intcomma('1234567890123456.78'))
print(intcomma(Decimal('1234567890123456.78')))

Observed:

1,234.12
1,234,567,890,123,456.8
1,234,567,890,123,456.78

Expected: grouping the large decimal string should retain its input digits, yielding 1,234,567,890,123,456.78. This is formatting without an explicit rounding request.

The string branch in src/humanize/number.py converts values containing a decimal point with float(value), then formats that rounded binary float. The final 7 is lost before grouping. The Decimal control shows the formatting path can preserve the value.