Avoid constrained types such as conint()

[multimeric]

Describe the bug
Python's type specification no longer allows for function calls directly in type annotations, as discussed here. However, in an effort to keep the generator compatible with Pydantic 1, constructions such as x: conint() are still created, which is not actually valid Python.

I think there needs to be a Pydantic 2+ flag that can relax the need for backwards compatibility, and use newer more valid constructs like Annotated[]

To Reproduce

Example schema:

openapi: 3.1.0
info:
  title: Constraints
  version: '1.0'
components:
  schemas:
    dayInYear:
      type: integer
      minimum: 1
      maximum: 365

Used commandline:

datamodel-codegen --input openapi.yml

Actual output

from __future__ import annotations

from pydantic import BaseModel, conint


class DayInYear(BaseModel):
    __root__: conint(ge=1, le=365)

Expected behavior
There should be a flag such as --pydantic-2 or --pydantic 2+ that instead outputs:

from typing_extensions import Annotated
from pydantic import BaseModel, Field

class DayInYear(BaseModel):
    __root__: Annotated[int, Field(ge=1, le=365)

Version:

• OS: Pop!_OS 22.04 LTS
• Python version: Python 3.13.1
• datamodel-code-generator version: 0.27.2

Additional context

• Update deprecated Pydantic v2 methods #2213 discusses some other issues caused when using Pydantic 2, although these deprecations are probably not as serious
• Generate Annotated types instead of root types for string constraints #2018 discusses how the output code can be much simpler and cleaner by embracing Annotated, although it doesn't discuss the context of deprecated syntax