Support python3.10 structural pattern matching (PEP 634-636)

[irgolic]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Feature

Python 3.10 introduces the new match syntax. https://peps.python.org/pep-0636/

Example:

num = 5

match num:
    case 5:
        print('is five')
    case default:
        print('is not five')

They support matching on custom classes too, with the __match_args__ attribute.

class MyClass:
    __match_args__ = ('num1', 'num2')

    def __init__(self, num1, num2):
        self.num1 = num1
        self.num2 = num2


myinstance = MyClass(5, 10)


match myinstance:
    case MyClass(5, num2):
        print(f'is 5 and {num2}')
    case MyClass(_, num2):
        print(f'is not 5 and is {num2}')

I've found myself adding this attribute to pydantic classes by hand, eventhough it seems pretty intuitive to me that the default behavior should match fields in the order that they were specified. So my code looks kind of like this:

class UpdateThing(BaseModel):
    __match_args__ = ("thing", "value")
    thing: Thing
    value: str


class AddThing(BaseModel):
    __match_args__ = ("index", "thing")
    index: int
    thing: Thing

Might as well add it natively?

I'm opening this issue to couple it with a PR :)