Handle non-finite values in naturalsize

[AnishPatel526]

Changes proposed in this pull request:

• naturalsize() now handles non-finite input consistently with the rest of the library. Every numeric formatter in humanize.number (ordinal, intcomma, intword, apnumber, fractional, scientific, clamp) already returns "NaN" / "+Inf" / "-Inf" for non-finite values via _format_not_finite. naturalsize() was the exception: naturalsize(float("nan")) raised ValueError: cannot convert float NaN to integer, and naturalsize(float("inf")) produced the bogus string "inf QB". It now returns "NaN" / "+Inf" / "-Inf".
• Added a parametrized test_naturalsize_non_finite covering nan, inf, -inf as both floats and strings; it fails on main and passes with this change.

Before

>>> import humanize
>>> humanize.naturalsize(float("nan"))
ValueError: cannot convert float NaN to integer
>>> humanize.naturalsize(float("inf"))
'inf QB'

After

>>> humanize.naturalsize(float("nan"))
'NaN'
>>> humanize.naturalsize(float("inf"))
'+Inf'
>>> humanize.naturalsize(float("-inf"))
'-Inf'

The fix reuses the existing humanize.number._format_not_finite helper so output matches the other formatters exactly, and guards right after the float(value) conversion. Finite values are unaffected.