rust-pyo3-sharedref: renamed UnsafePyLeaked to SharedByPyObject Rationale: - the object itself is not unsafe, only most of its methods are. This is similar to raw pointers: obtaining them is not unsafe, using them is. That being said, we are not ready yet to declare, e.g, `borrow_with_owner()` safe because that gives an early warning to users. - it was not really a leak, as the data is actually owned by a Python object on which we keep a (Python) reference with proper increment of the refcount. Hence the terminology was too much of a deterrent. We hope that the new terminology conveys both that the data contains a shared reference and that it was generously lended by a Python object. The `SharedByPyObjectRef` name is arguably heavy, but it is merely an implementation detail that users will not be much exposed to, thanks to the `Deref` implementation. As previously, we keep the changes in tests to a minimum, to make obvious in the diff that the tests have not changed. We will take care of renaming their local variables and functions in a later move.