PerspectiveWidget support for new Python API

[texodus]

Adds

• Support for PerspectiveWidget. Lots of small changes applied, most notably removal of client-only e.g. client=True mode, but some care has been taken to maintain the rudiments of 2.10.1's user-facing API, at least so far. I would like to consider removing the ViewConfig traitlets as well in the future, as restore() is the preferred way to do this from both a usability and performance pov. This component needs a lot more cleanup, this PR just updates the internal API relevant parts.
• Proper packaging of perspective-jupyterlab client extension assets. These now use maturin's data directory support to package the assets, which are built using jupyter-packaging's labextension install webpack builder.
• Manylinux builds for linux.
• aarch64 builds for OSX. I've also added support for this architecture on Linux Provide linux aarch64 wheels #2221, but it is not yet enabled on CI (and hence will not distribute), as I am not sure how we can test it just yet. Suggestions welcome.
• A rewrite of the project's Github Actions CI script which is substantially faster. The first part of this work was merged in Docs and examples update for new API #2659, but as we did not yet have support for PerspectiveWidget, these steps were omitted from this PR and included here.
• perspective-server and perspective-client have been reorganized to allow a new variant of the Session type introduced in Perspective Virtual API (Python) #2625, ProxySession, which allows an existing Client instance to itself act as a Session for another Client. This change was necessary to support PerspectiveWidget, as the API was designed for (and remains convenient for) working on Table instances directly, for which the new API prevents access to the originating Server.
• Removed a number of unused build automations scripts and removed some crufty code generation, such as _version.py in the Python package.
• Fix perspective-jupyterlab and perspective-python dependency ranges to allow JupyterLab 4. This was already technically supported but will no longer warn of version mismatches.