support for PyFrame functions

[dsal3389]

Hello!
I am in the process of writing a python profiler in Rust and I thought it would be a good starting point to
get my toes in pyo3

use case

the sys.setprofile/threading.setprofile function takes a callable that should accept Frame as first argument, the equivalent pyo3 type for frame is the PyFrame, the rust function I pass to setprofile is like so

fn handle(
    frame: Bound<'_, pyo3::types::PyFrame,
    event: ProfilerEvent,  // implementes `FromPyObject`
    args: Bound<'_, PyAny>
) {
    ...
}

problem

unfortunately Bound does not implement PyFrameMethods for Bound<'py, PyFrame> and there is no such trait as PyFrameMethods to be implemented, so I can't access frame functions

(I am still in the process of understanding pyo3 so I might be wrong here)
I tried to use the ffi function directly; PyFrame_GetLineNumber for example, but it expect *mut PyFrameObject which is the underlying ffi object, and I don't have any way to get that ffi object since it is behind the Bound struct

implementation

create PyFrameMethods and implement it on Bound<'py, PyFrame>, since as_ptr cannot be used on PyFrame because as_ptr returns ffi::PyObject and we need PyFrameObject, a new function should be implemented on PyFrame to return the ffi type, and PyFrame struct member should be ffi:PyFrameObject instead of PyAny

---

I would be glad to take on this implementation

Do you need mentoring?

It would be helpful, yes

[ngoldbaum]

It looks like the existing safe rust wrappers are pretty minimal: https://github.com/PyO3/pyo3/blob/f89b5f71ddb3f482256a7a2f4da5bc8b84db19a5/src/types/frame.rs

It looks like you can also add wrappers for PyFrameLocalsProxy_Type on 3.13 and newer.

Adding more full-featured safe wrappers for the PyFrame API seems worth doing for use-cases like yours.

[ngoldbaum]

see also #4762