Function extract_derive_plugins 

pub fn extract_derive_plugins(attrs: &[Attribute]) -> Vec<PluginRef>

Extract plugin references from #[facet(derive(Plugin1, Plugin2, ...))] attributes.

Supports both simple names and explicit paths:

• #[facet(derive(Error))] → PluginRef::Simple("Error")
• #[facet(derive(some_crate::SomeTrait))] → PluginRef::Path { crate_name: "some_crate", plugin_name: "SomeTrait" }