[SPARK-58312][PYTHON] Remove unnecessary type: ignore comments in pyspark.sql.udf and group

[Spenserrrr]

What changes were proposed in this pull request?

Several # type: ignore comments in python/pyspark/sql/udf.py and python/pyspark/sql/group.py can be removed by fixing the underlying type issues:

• In UDFRegistration.register, a UDF is built and wrapped by _create_udf, then immediately unwrapped via the ._unwrapped attribute. Building the UserDefinedFunction directly removes this round-trip and 2 [attr-defined] ignores.
• In group.py, the @dfapi/@df_varargs_api decorated methods intentionally have docstring-only bodies and trigger 6 [empty-body] ignores. These are replaced by a single file-level disable-error-code directive, matching the style already used in dataframe.py, column.py, window.py, and table_arg.py.

Why are the changes needed?

To improve readability

Does this PR introduce any user-facing change?

No

How was this patch tested?

Existing tests. mypy --config-file python/mypy.ini python/pyspark passes at full scope.

Was this patch authored or co-authored using generative AI tooling?

No

[Spenserrrr]

@gaogaotiantian

[uros-b]

LGTM, thank you @Spenserrrr! also, cc @HyukjinKwon @Yicong-Huang