Return non-finite floats unchanged from naturaldelta

[eeshsaxena]

Summary

Fixes #333.

naturaldelta() documents that a value which cannot be converted to a number is "returned unchanged." float("nan") is handled (its int() raises ValueError, which is caught), but float("inf")/float("-inf") raise an uncaught OverflowError from int(value), because the except (ValueError, TypeError) clause omitted OverflowError. The behavior was asymmetric and contradicted the docstring.

Before

>>> humanize.naturaldelta(float("nan"))
'nan'
>>> humanize.naturaldelta(float("inf"))
OverflowError: cannot convert float infinity to integer

After

>>> humanize.naturaldelta(float("inf"))
'inf'
>>> humanize.naturaldelta(float("-inf"))
'-inf'

Implementation note

The catch is scoped to the int(value) guard only. A finite value too large to convert to a datetime.timedelta (e.g. 1e40) still raises OverflowError from timedelta(), as documented under Raises: - this is verified by an added test so the non-finite guard does not swallow the legitimate overflow.

Tests

Added test_naturaldelta_nonfinite (nan, inf, -inf returned unchanged) and test_naturaldelta_overflow (finite 1e40 still raises OverflowError). Full tests/test_time.py passes (387 passed).