Exclude decimal.Decimal from built-in BSON checks

Author: NoahStapp

bson/__init__.py

@@ -920,8 +920,8 @@ def _encode_maxkey(name: bytes, dummy0: Any, dummy1: Any, dummy2: Any) -> bytes:
     if hasattr(_typ, "_type_marker"):
         _MARKERS[_typ._type_marker] = _ENCODERS[_typ]
 
-
-_BUILT_IN_TYPES = tuple(t for t in _ENCODERS)
+# Exclude decimal.Decimal since auto-conversion is explicitly opt-in.
+_BUILT_IN_TYPES = tuple(t for t in _ENCODERS if t != decimal.Decimal)
 
 
 def _name_value_to_bson(

test/test_bson.py

@@ -1237,7 +1237,7 @@ def test_codec_options_repr(self):
             "unicode_decode_error_handler='strict', "
             "tzinfo=None, type_registry=TypeRegistry(type_codecs=[], "
             "fallback_encoder=None), "
-            "datetime_conversion=DatetimeConversion.DATETIME)"
+            "datetime_conversion=DatetimeConversion.DATETIME, convert_decimal=False)"
         )
         self.assertEqual(r, repr(CodecOptions()))