Reject DecimalType with precision larger than 38

The Iceberg spec requires decimal precision to be 38 or less, but
DecimalType(39, 0) (and parsing 'decimal(39, 0)') was accepted silently,
producing a value not representable in decimal's fixed-byte storage. Validate
precision <= 38 in DecimalType.__init__, matching the Java reference which
raises for precision > 38.

Closes #3583

Author: kratos0718

pyiceberg/types.py

@@ -324,6 +324,8 @@ class DecimalType(PrimitiveType):
     root: tuple[int, int]
 
     def __init__(self, precision: int, scale: int) -> None:
+        if precision > 38:
+            raise ValueError(f"Decimals with precision larger than 38 are not supported: {precision}")
         super().__init__(root=(precision, scale))
 
     @model_serializer

tests/test_types.py

@@ -147,6 +147,15 @@ def test_decimal_type() -> None:
     assert type_var == pickle.loads(pickle.dumps(type_var))
 
 
+def test_decimal_type_rejects_precision_over_38() -> None:
+    # The Iceberg spec requires decimal precision to be 38 or less; the Java
+    # reference implementation raises for precision > 38. See issue #3583.
+    with pytest.raises(ValueError, match="precision larger than 38 are not supported: 39"):
+        DecimalType(39, 0)
+    # Boundary: precision exactly 38 is still valid.
+    assert DecimalType(38, 0).precision == 38
+
+
 def test_struct_type() -> None:
     type_var = StructType(
         NestedField(1, "optional_field", IntegerType(), required=True),