Remove pyo3 in runtime and daemon as it generates `libpython` dependencies

Previous implementation of the runtime would link `libpython` even though it
might not be required.

This commit put pyo3 dependency under a feature flag that is only active if
the runtime is called from python for a python operator.

This fix:
- https://github.com/dora-rs/dora/actions/runs/4879188973/jobs/8705515472
- https://github.com/dora-rs/dora/issues/280#issuecomment-1534058207
- and https://github.com/dora-rs/dora-drives/issues/58#event-9162532660

apis/python/node/Cargo.toml

@@ -20,7 +20,7 @@ pyo3 = { version = "0.18", features = ["eyre", "abi3-py37"] }
 eyre = "0.6"
 serde_yaml = "0.8.23"
 flume = "0.10.14"
-dora-runtime = { workspace = true, features = ["tracing"] }
+dora-runtime = { workspace = true, features = ["tracing", "python"] }
 arrow = { version = "35.0.0", features = ["pyarrow"] }
 
 [lib]

binaries/runtime/Cargo.toml

@@ -28,7 +28,7 @@ serde_yaml = "0.8.23"
 tokio = { version = "1.24.2", features = ["full"] }
 tokio-stream = "0.1.8"
 # pyo3-abi3 flag allow simpler linking. See: https://pyo3.rs/v0.13.2/building_and_distribution.html
-pyo3 = { version = "0.18", features = ["eyre", "abi3-py37"] }
+pyo3 = { version = "0.18", features = ["eyre", "abi3-py37"], optional = true }
 tracing = "0.1.36"
 tracing-subscriber = "0.3.15"
 dora-download = { workspace = true }
@@ -41,3 +41,4 @@ default = ["tracing"]
 tracing = ["dora-tracing"]
 telemetry = ["tracing", "opentelemetry", "tracing-opentelemetry"]
 metrics = ["opentelemetry", "opentelemetry-system-metrics", "dora-metrics"]
+python = ["pyo3"]

binaries/runtime/src/operator/mod.rs

@@ -9,6 +9,7 @@ use std::any::Any;
 use tokio::sync::{mpsc::Sender, oneshot};
 
 pub mod channel;
+#[cfg(feature = "python")]
 mod python;
 mod shared_lib;
 
@@ -36,7 +37,9 @@ pub fn run_operator(
                 )
             })?;
         }
+        #[allow(unused_variables)]
         OperatorSource::Python(source) => {
+            #[cfg(feature = "python")]
             python::run(
                 node_id,
                 &operator_definition.id,
@@ -51,6 +54,10 @@ pub fn run_operator(
                     operator_definition.id
                 )
             })?;
+            #[cfg(not(feature = "python"))]
+            tracing::error!(
+                "Dora runtime tried spawning Python Operator outside of python environment."
+            );
         }
         OperatorSource::Wasm(_) => {
             tracing::error!("WASM operators are not supported yet");