DataFrame.groupby.agg with unpacking a dict

[loicdiridollou]

Describe the bug
A clear and concise description of what the bug is.

It seems like we are missing some overloads for aggregate in groupby when we use unpacking of dictionary.
The other issue is that is seems like pyright and mypy are not recognizing the same type when unpacking a dictionary, mypy reads it correctly as tuple[str, dict[str, str]] while pyright sees it as dict[str, str].
Considering this issue is it something we would like to support and if so at what cost?

To Reproduce

1. Provide a minimal runnable pandas example that is not properly checked by the stubs.
2. Indicate which type checker you are using (mypy or pyright).
3. Show the error message received from that type checker while checking your example.

import pandas as pd

df = pd.DataFrame(
    {
        "a": [1, 2, 3],
        "b": [4, 5, 6],
        "c": [7, 8, 9],
    }
)

dico = {"a":("a", "mean")}

df.groupby("b").agg(a= ("a", "mean"))  # passes fine
df.groupby("b").agg(**dico)  # create warnings and fails linter 

This is the errors:

/Users/loic/Documents/Code/pandas-stubs/main/tests/test_frame.py
  /Users/loic/Documents/Code/pandas-stubs/main/tests/test_frame.py:4705:5 - error: No overloads for "aggregate" match the provided arguments (reportCallIssue)
  /Users/loic/Documents/Code/pandas-stubs/main/tests/test_frame.py:4705:27 - error: Argument of type "tuple[str, str]" cannot be assigned to parameter "func" of type "Literal['size']" in function "aggregate"
    "tuple[str, str]" is not assignable to "Literal['size']" (reportArgumentType)
2 errors, 0 warnings, 0 informations

tests/test_frame.py:4705: error: No overload variant matches argument type "dict[str, tuple[str, str]]"  [call-overload]
tests/test_frame.py:4705: note: Possible overload variants:
tests/test_frame.py:4705: note:     def aggregate(self, func: Literal['size']) -> Series[Any]
tests/test_frame.py:4705: note:     def aggregate(self, func: Callable[..., Any] | str | ufunc | list[Callable[..., Any] | str | ufunc] | Mapping[Any, Callable[..., Any] | str | ufunc | list[Callable[..., Any] | str | ufunc]] | None = ..., *args: Any, engine: Literal['cython', 'numba'] | None = ..., engine_kwargs: _WindowingNumbaKwargs | None = ..., **kwargs: Any) -> DataFrame

Please complete the following information:

• OS: MacOS
• OS Version 15.6.1
• python version 3.13
• version of type checker 1.17.1
• version of installed pandas-stubs main

Additional context
Add any other context about the problem here.

[Dr-Irv]

Had to experiment a bit.

In core/groupby/generic.pyi, for DataFrameGroupby.aggregate(), if you add this overload at the end, it solves the problem for your example:

    @overload
    def aggregate(
        self,
        func: AggFuncTypeFrame | None = None,
        /,
        **kwargs,
    ) -> DataFrame: ...

PR welcome with test.

[loicdiridollou]

Great job! Thanks for the suggestion, that was indeed the solution, will keep it in the back of my mind for the next issue.