Describe the bug
Some iterators and enter-exit context manager does not implement keep alive policy to bindings.
https://pybind11.readthedocs.io/en/stable/advanced/functions.html?highlight=keep_alive#keep-alive

To Reproduce
See Path.Iter implementation for example.

Expected behavior
There should be py::keep_alive<0, 1>() policy.

Desktop (please complete the following information):

• OS: macOS 10.15.5
• Architecture x86_64
• Python 3.7
• skia-python version v0.0.5

Additional context
n/a