Use py.new_pool() to bound pyo3 variable

To alievate the unbounded memory growth, we're replacing variable dereferencing
with scoped `GILPool` as described in the pyo3 documentation recently updated. See:
PyO3/pyo3#2864

binaries/runtime/src/operator/python.rs

@@ -10,7 +10,7 @@ use dora_message::uhlc;
 use dora_node_api::communication::Publisher;
 use dora_operator_api_python::metadata_to_pydict;
 use dora_operator_api_types::DoraStatus;
-use eyre::{bail, eyre, Context};
+use eyre::{bail, eyre, Context, Result};
 use pyo3::{
     ffi, pyclass,
     types::IntoPyDict,
@@ -137,7 +137,9 @@ pub fn spawn(
             };
             input.metadata.parameters.open_telemetry_context = Cow::Owned(string_cx);
 
-            let status_enum = Python::with_gil(|py| {
+            let status = Python::with_gil(|py| -> Result<i32> {
+                let pool = unsafe { py.new_pool() };
+                let py = pool.python();
                 let input_dict = PyDict::new(py);
                 let bytes = PyBytes::new(py, &input.data());
 
@@ -147,18 +149,15 @@ pub fn spawn(
 
                 let status_enum = operator
                     .call_method1(py, "on_input", (input_dict, send_output.clone()))
-                    .map_err(traceback);
-
-                unsafe {
-                    ffi::Py_DECREF(bytes.as_ptr());
-                    ffi::Py_DECREF(input_dict.as_ptr());
-                }
-                status_enum
+                    .map_err(traceback)?;
+
+                let status_val = status_enum
+                    .getattr(py, "value")
+                    .wrap_err("on_input must have enum return value")?;
+                status_val
+                    .extract(py)
+                    .wrap_err("on_input has invalid return value")
             })?;
-            let status_val = Python::with_gil(|py| status_enum.getattr(py, "value"))
-                .wrap_err("on_input must have enum return value")?;
-            let status: i32 = Python::with_gil(|py| status_val.extract(py))
-                .wrap_err("on_input has invalid return value")?;
             match status {
                 s if s == DoraStatus::Continue as i32 => {} // ok
                 s if s == DoraStatus::Stop as i32 => break StopReason::ExplicitStop,