refactor: add a mixin for int enum field custom

Makefile

@@ -79,7 +79,7 @@ docs: deps
 _style:
 	isort -src $(checkfiles)
 	black $(checkfiles)
-style: _style deps
+style: deps _style
 
 build: deps
 	rm -fR dist/

examples/enum_fields.py

@@ -1,6 +1,7 @@
 from enum import Enum, IntEnum
 
 from tortoise import Tortoise, fields, run_async
+from tortoise.fields.data import IntEnumFieldMixin, IntField
 from tortoise.models import Model
 
 
@@ -16,18 +17,34 @@ class Currency(str, Enum):
     USD = "USD"
 
 
+class Protocol(IntEnum):
+    A = 10000
+    B = 80000
+
+
+class Int32EnumInstance(IntEnumFieldMixin, IntField):
+    pass
+
+
+def Int32EnumField(enum_type, **kwargs):
+    return Int32EnumInstance(enum_type, **kwargs)
+
+
 class EnumFields(Model):
     service: Service = fields.IntEnumField(Service)
     currency: Currency = fields.CharEnumField(Currency, default=Currency.HUF)
+    protocol: Protocol = Int32EnumField(Protocol)
 
 
 async def run():
     await Tortoise.init(db_url="sqlite://:memory:", modules={"models": ["__main__"]})
     await Tortoise.generate_schemas()
 
-    obj0 = await EnumFields.create(service=Service.python_programming, currency=Currency.USD)
+    obj0 = await EnumFields.create(
+        service=Service.python_programming, currency=Currency.USD, protocol=Protocol.A
+    )
     # also you can use valid int and str value directly
-    await EnumFields.create(service=1, currency="USD")
+    await EnumFields.create(service=1, currency="USD", protocol=Protocol.B.value)
 
     try:
         # invalid enum value will raise ValueError