CI tests for plugins

[nightlark]

Currently, things under the plugins folder are untested -- a GitHub Actions CI workflow should be created that at minimum makes sure they can be pip installed, and ideally would try running them on a test file that uses the plugin functionality.

A first pass could look be a workflow that for each subdirectory in the plugins folder (perhaps with a list of directories to ignore):

• creates a fresh Python venv (look at using uv -- it is fast)
• install Surfactant
• install the plugin
• try running the plugin on some test files to make sure the plugin at least doesn't crash...
• ideally: compare the generated SBOM against the expected output