bindings: python: fix tp_dealloc callbacks in all objects
bindings: python: fix tp_dealloc callbacks in all objects

We have a significant memory leak in the current implementation as we
don't call PyObject_Del() as the last action in tp_dealloc callbacks.

From tp_dealloc's documentation:

---
The destructor function should free all references which the instance
owns, free all memory buffers owned by the instance (using the freeing
function corresponding to the allocation function used to allocate the
buffer), and finally (as its last action) call the type’s tp_free
function.
---

PyObject_Del() will internally call the tp_free callback of the type.
Add a call to it as the last action in every destructor.

Fixes: 96c524c4951c ("bindings: implement python bindings")
Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod