feat: custom node (#138)

* feat: custom node

* add zen template, expose $nodes and $root

* add custom handler to go and nodejs

* add support for python, improve bindings, add error to zen template

* fix: correct binding exports for nodejs and python

* fix benchmark

* improve rust api, trim template in zen templates

* update cargo action

* update expression version

* compile action

* fix action format

bindings/python/src/custom_node.rs

@@ -0,0 +1,42 @@
+use anyhow::anyhow;
+use pyo3::types::PyDict;
+use pyo3::{PyObject, Python};
+use pythonize::depythonize;
+
+use zen_engine::handler::custom_node_adapter::{CustomNodeAdapter, CustomNodeRequest};
+use zen_engine::handler::node::{NodeResponse, NodeResult};
+
+use crate::types::PyNodeRequest;
+
+#[derive(Default)]
+pub(crate) struct PyCustomNode(Option<PyObject>);
+
+impl From<PyObject> for PyCustomNode {
+    fn from(value: PyObject) -> Self {
+        Self(Some(value))
+    }
+}
+
+impl From<Option<PyObject>> for PyCustomNode {
+    fn from(value: Option<PyObject>) -> Self {
+        Self(value)
+    }
+}
+
+impl CustomNodeAdapter for PyCustomNode {
+    async fn handle(&self, request: CustomNodeRequest<'_>) -> NodeResult {
+        let Some(callable) = &self.0 else {
+            return Err(anyhow!("Custom node handler not provided"));
+        };
+
+        let content: NodeResponse = Python::with_gil(|py| {
+            let req = PyNodeRequest::from_request(py, request)?;
+            let result = callable.call1(py, (req,))?;
+
+            let dict = result.extract::<&PyDict>(py)?;
+            depythonize(dict)
+        })?;
+
+        Ok(content)
+    }
+}