… prefix on some funcs

- Remove dangling pointer to callback on cplugin unload
- Remove need to allocate DeviceInfo in rust from a c plugin. We just let them use the FFI type and we copy the data over
- Add some const qualifiers to things that should never be mutated

* Simplify CMakeLists for test_c_plugin
It no longer needs linking against Rust code

* Remove new_device_info & drop_device_info

* Bump CPLUGIN_ABI_VERSION since everything's definitely incompatible now

* Fix "bindings changed"

* Also run workflow on PR