@model_validator(mode="after") is not class methdod

[koxudaxi]

Describe the bug

@model_validator(mode="after") decorates an instance method instead of a class method that receives the raw values (the case for mode="before").

Related Issues: koxudaxi/datamodel-code-generator#1448

https://docs.pydantic.dev/latest/usage/validators/#model-validators

To Reproduce
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4. See error

Expected behavior
@model_validator(mode="after") work as instance method

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Environments (please complete the following information):

• IDE: [e.g. PyCharm Community 2022.1 ]
• OS: [e.g. macOS 12.2.0 ]
• Pydantic Version [e.g. 1.9.0 ]
• Plugin version [e.g. 0.3.11 ]

Additional context
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