Make Not expression JSON serializable

[Aniketsy]

#2520

This PR makes the Not boolean expression in pyiceberg JSON serializable using Pydantic

Please let me know if my approach or fix needs any improvements . I’m open to feedback and happy to make changes based on suggestions.
Thank you !

[rambleraptor]

Can you write a test for:

• Converting a Not Expression to JSON
• Converting a JSON Not Expression -> Python Not Expression

This does just enough Pydantic magic that I'm concerned about potential side-effects and a test will help ground us.

[Aniketsy]

@rambleraptor I have updated with changes, please let me know if this needs improvement. Thanks!

[Aniketsy]

@kevinjqliu could you please review these changes, not sure ci check fails are related to this.

[Fokko]

I think we still need the __new__ method, how about:

class Not(IcebergBaseModel, BooleanExpression):
    """NOT operation expression - logical negation."""
    model_config = ConfigDict(arbitrary_types_allowed=True)

    type: TypingLiteral["not"] = Field(default="not")
    child: BooleanExpression = Field()

    def __init__(self, child: BooleanExpression, **_) -> None:
        super().__init__(child=child)

    def __new__(cls, child: BooleanExpression, **_) -> BooleanExpression:  # type: ignore
        if child is AlwaysTrue():
            return AlwaysFalse()
        elif child is AlwaysFalse():
            return AlwaysTrue()
        elif isinstance(child, Not):
            return child.child
        obj = super().__new__(cls)
        return obj

[Aniketsy]

sure, i'll update and test it.