fix(intcomma): handle scientific notation for large/small floats

Fixes #431 - intcomma() returns scientific notation for floats of 1e16 and
above (and very small floats like 1e-5), with no commas added.

Root cause: Python's repr() switches to scientific notation for floats with
magnitude >= 1e15 or <= 1e-5. The f"{value:,}" format specifier uses repr()
internally, so comma formatting is never applied to the exponent form.

Fix: When ndigits is None and the float is a whole number, format as int to
avoid trailing .0. When the float would be formatted in scientific notation,
use Decimal for a proper decimal representation before applying commas.

Author: Jah-yee

src/humanize/number.py

@@ -197,7 +197,26 @@ def intcomma(value: NumberOrString, ndigits: int | None = None) -> str:
     if ndigits is not None:
         result = f"{value:,.{ndigits}f}"
     else:
-        result = f"{value:,}"
+        if isinstance(value, float) and value == int(value):
+            # Whole-number float: format as int to avoid trailing .0
+            result = f"{int(value):,}"
+        elif isinstance(value, float) and value != 0 and (abs(value) >= 1e15 or abs(value) <= 1e-5):
+            # Python repr uses scientific notation for very large/small floats,
+            # which breaks the , format specifier. Use Decimal for proper formatting.
+            from decimal import Decimal
+            d = Decimal(str(value))
+            formatted = f"{d:f}"
+            if "." in formatted:
+                int_part, dec_part = formatted.split(".")
+                dec_part = dec_part.rstrip("0")
+                if dec_part:
+                    result = f"{int(int_part):,}.{dec_part}"
+                else:
+                    result = f"{int(int_part):,}"
+            else:
+                result = f"{int(formatted):,}"
+        else:
+            result = f"{value:,}"
     if thousands_sep != "," or decimal_sep != ".":
         result = result.translate(str.maketrans(",.", thousands_sep + decimal_sep))
     return result