feat(python): class method attribute

[dbrattli]

What

• Add support for [<Py.Decorate>] attribute on (static) methods (previously only worked on classes)
• Add new [<Py.ClassMethod>] attribute to emit @classmethod instead of @staticmethod

[<Py.Decorate>] now works on:

• Classes (as before)
• Static methods
• Instance methods
• Properties

This enables integration with Python frameworks like Pydantic that require method-level decorators:

  [<AttachMembers>]
  type User(Name: string) =
      inherit BaseModel()
      member val Name = Name with get, set

      [<Py.Decorate("pydantic.field_validator", "'Name'")>]
      [<Py.ClassMethod>]
      static member validate_name(cls: obj, v: string) = v.ToUpper()

Generates:

  class User(BaseModel):
      Name: str

      @field_validator('Name')
      @classmethod
      def validate_name(cls, v: str) -> str:
          return v.upper()