[SPARK-50467][PYTHON] Add __all__ for builtin functions

### What changes were proposed in this pull request?
Add `__all__` for builtin function

### Why are the changes needed?
to control the wild import

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?
ci and manual test

### Was this patch authored or co-authored using generative AI tooling?
no

Closes apache#49024 from zhengruifeng/py_func_all.

Authored-by: Ruifeng Zheng <[email protected]>
Signed-off-by: Ruifeng Zheng <[email protected]>