test: add tests for Decimal/Fraction types and edge cases to improve diff coverage

- Add tests for get_xml_type with Decimal and Fraction (numbers.Number subclasses)
- Add test for parallel processing with root and primitive values
- Add test for get_optimal_workers in non-free-threaded mode
- Coverage improved to 99% (393 total statements, only 2 uncovered)
- All ruff and ty checks pass

Amp-Thread-ID: https://ampcode.com/threads/T-ab40799c-7282-451b-bdf6-4a74c73a62b7
Co-authored-by: Amp <amp@ampcode.com>

Author: vinitkumar

tests/test_dict2xml.py

@@ -1142,3 +1142,26 @@ def test_make_attrstring_function_directly(self) -> None:
         empty_attrs: dict[str, Any] = {}
         result = make_attrstring(empty_attrs)
         assert result == ""
+
+    def test_get_xml_type_with_decimal(self) -> None:
+        """Test get_xml_type with Decimal (numbers.Number subclass)."""
+        from decimal import Decimal
+
+        result = dicttoxml.get_xml_type(Decimal("3.14"))
+        assert result == "number"
+
+    def test_get_xml_type_with_fraction(self) -> None:
+        """Test get_xml_type with Fraction (numbers.Number subclass)."""
+        from fractions import Fraction
+
+        result = dicttoxml.get_xml_type(Fraction(1, 2))
+        assert result == "number"
+
+    def test_convert_with_decimal(self) -> None:
+        """Test converting Decimal values."""
+        from decimal import Decimal
+
+        data = {"value": Decimal("123.456")}
+        result = dicttoxml.dicttoxml(data, attr_type=True)
+        assert b"123.456" in result
+        assert b'type="number"' in result

tests/test_parallel.py

@@ -323,3 +323,23 @@ def test_parallel_with_datetime_values(self) -> None:
         result_parallel = dicttoxml.dicttoxml(data, parallel=True, workers=4)
         result_serial = dicttoxml.dicttoxml(data, parallel=False)
         assert result_parallel == result_serial
+
+    def test_parallel_with_root_and_primitive(self) -> None:
+        """Test parallel processing with root element and primitive value."""
+        data = 123
+        result = dicttoxml.dicttoxml(data, root=True, parallel=True, workers=4)
+        assert b"<?xml version" in result
+        assert b"123" in result
+        assert b"<root" in result
+
+    def test_get_optimal_workers_in_non_free_threaded(self) -> None:
+        """Test get_optimal_workers returns min(4, cpu_count) in non-free-threaded mode."""
+        import os
+        from unittest.mock import patch
+
+        cpu_count = os.cpu_count() or 4
+        expected = min(4, cpu_count)
+
+        with patch('json2xml.parallel.is_free_threaded', return_value=False):
+            result = get_optimal_workers(None)
+            assert result == expected