Refactor method classification logic: __new__ methods are now classified as staticmethod

[cake-monotone]

Summary

__new__ methods are technically static methods, with cls as their first argument. However, Ruff currently classifies them as classmethod, which causes two issues:

• It conveys incorrect information, leading to confusion. For example, in cases like ARG003, __new__ is explicitly treated as a classmethod.
• Future rules that should apply to staticmethod may not be applied correctly due to this misclassification.

Based on #13154, I have excluded the first argument cls of __new__ from ARG004. (not concluded, it can be change)

Closes #13154

[github-actions]

ruff-ecosystem results

Linter (stable)

ℹ️ ecosystem check detected linter changes. (+0 -2 violations, +0 -0 fixes in 1 projects; 53 projects unchanged)

pandas-dev/pandas (+0 -2 violations, +0 -0 fixes)

- pandas/core/groupby/grouper.py:258:13: PLW0642 Reassigned `cls` variable in class method
- pandas/io/excel/_base.py:1178:13: PLW0642 Reassigned `cls` variable in class method

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
PLW0642	2	0	2	0	0

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+0 -2 violations, +0 -0 fixes in 1 projects; 53 projects unchanged)

pandas-dev/pandas (+0 -2 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

- pandas/core/groupby/grouper.py:258:13: PLW0642 Reassigned `cls` variable in class method
- pandas/io/excel/_base.py:1178:13: PLW0642 Reassigned `cls` variable in class method

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
PLW0642	2	0	2	0	0

[cake-monotone]

I'm sure there are other breaking changes besides the ruff-ecosystem results
I'll try to summarize them.

[cake-monotone]

Affected Rules

• ARG003: unused-class-method-argument
• ARG004: unused-static-method-argument
• PLW0642: self-or-cls-assignment
• PLW0211: bad-staticmethod-argument
• N804: invalid-first-argument-name-for-class-method
• PLR0913: too-many-arguments
• PLR0917: too-many-positional-arguments

ARG003, ARG004

ARG003 (unused-class-method-argument) -> ARG004 (unused-static-method-argument)

PLW0642

__new__ methods will no longer be checked by PLW0642. This rule only applies to methods and class methods, not static methods.

N804, PLW0211

N804 (invalid-first-argument-name-for-class-method) -> PLW0211 (bad-staticmethod-argument)

PLR0913, PLR0917

PLR0913 (too-many-arguments) and PLR0917 (too-many-positional-arguments) behave differently for classmethod and staticmethod. In classmethod, the first argument cls is excluded from the argument count. In staticmethod, cls is not excluded, so the argument limit applies more strictly.

Example

You can view an example of how these rules are applied here:
https://play.ruff.rs/2df5f2b6-093f-4988-a562-c6101a1c71cc

class ClassDunderNew:
    @classmethod
    def __new__(
        cls,
        x,  # ARG003: Unused class method argument: `x`
    ):
        cls = 1  # PLW0642: Reassigned `cls` variable in class method

    @classmethod
    def __new__(  # PLR0913: Too many arguments in function definition (6 > 5)  # PLR0917: Too many positional arguments (6/5)
        self,  # N804: First argument of a class method should be named `cls`
        a1, a2, a3, a4, a5,
        a6,
    ):
        ...


class StaticDunderNew:
    @staticmethod
    def __new__(
        cls,
        x,  # ARG004: Unused static method argument: `x`
    ):
        cls = 1

    @staticmethod
    def __new__(  # PLR0913: Too many arguments in function definition (6 > 5)  # PLR0917: Too many positional arguments (6/5)
        self,  # PLW0211: First argument of a static method should not be named `self`
        a1, a2, a3, a4, a5,
    ):
        ...

[cake-monotone]

I reviewed all the code affected by function_type::classify. Let me know if I missed any affected rules.

Please check if these affected rules are acceptable. :)