Bump pyo3 0.24 -> 0.29 so symclaw-python builds on Python 3.14

The bindings could not build against the installed interpreter, so the
whole workspace had to be checked with --exclude symclaw-python. Two API
changes: PyObject left the prelude (now Py<PyAny>), and #[pyclass] types
implementing Clone must opt in to the FromPyObject derive.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

crates/symclaw-python/Cargo.toml

@@ -14,6 +14,6 @@ crate-type = ["cdylib"]
 
 [dependencies]
 symclaw-core = { path = "../symclaw-core" }
-pyo3 = { version = "0.24", features = ["extension-module"] }
+pyo3 = { version = "0.29", features = ["extension-module"] }
 num-rational = { workspace = true }
 ordered-float = { workspace = true }

crates/symclaw-python/src/lib.rs

@@ -163,7 +163,7 @@ fn py_to_expr(obj: &Bound<'_, PyAny>) -> PyResult<Arc<Expr>> {
 // ── PyExpr ───────────────────────────────────────────────────────
 
 /// A Python-facing symbolic expression.
-#[pyclass(name = "Expression")]
+#[pyclass(name = "Expression", from_py_object)]
 #[derive(Clone)]
 struct PyExpr {
     inner: Arc<Expr>,
@@ -482,7 +482,7 @@ impl PyLimitResult {
 /// Create symbol(s). Single name returns Expression, comma-separated returns tuple.
 #[pyfunction]
 #[pyo3(name = "S")]
-fn py_s(py: Python<'_>, names: &str) -> PyResult<PyObject> {
+fn py_s(py: Python<'_>, names: &str) -> PyResult<Py<PyAny>> {
     let parts: Vec<&str> = names
         .split(',')
         .map(str::trim)