Experiment moving pinns functionality into conmonrs

[pinns](https://github.com/cri-o/cri-o/tree/main/pinns) is a utility called by cri-o to create pod-level namespaces. It would be cool if conmon-rs could create those namespaces for the pod. Most notably, if it could manage a `pause` process to hold open the pod's PID namespace, then CRI-O could get rid of the infra container

Start by reading the pinns utility in the linked cri-o/pinns path and the conmon-rs entry points involved in pod setup. Determine how pod-level namespaces and a pause process would be managed, and define the integration boundary before implementing anything. Done means conmon-rs can hold the pod PID namespace open without an infra container.

Written by the indexing model from the issue text.