fully self contained python client

## Use Case

agave python client could be a self contained rendering system for python

## Solution

a fully headless agave python client that uses the code in renderlib, exclusively the vulkan backend, and doesn't need websockets or Qt. It should just pass commands directly from python to c++ code, using the current command api as expressed in agave.py and command.h. We can introduce a new build target that builds the python integration library into the python package and bundles it together. It should use nanobind as the python-to-c++ bridge.

## Alternatives

api redesign

Read agave.py and command.h first, then inspect renderlib and the existing build targets. Determine how the current command API maps from Python to C++ and how the Python package is assembled. Done means a headless bundled Python client using renderlib's Vulkan backend, nanobind, and no WebSockets or Qt.

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