feat(functions): expose retry policies in Python and Rust (#4873)

Expose `FunctionRetryPolicy` on Function declarations and refresh
overrides, together with `error_policy` and recorded attempt counts.
Python uses the Rust validation rules before sending a request; local
refreshes reject these Enterprise options.

The policy bounds calls and backoff, supports
class/message/provider-code matching, and can disable retries with
`max_attempts=1`. Batch retry and skip operate on the whole failed call.
Requires Enterprise server support for the new policy.

Validation: rebuilt the Python extension; 47 targeted Python tests and
10 Rust tests passed. Python `make check`, Rust formatting, and `cargo
clippy --features remote --tests --examples -- -D warnings` passed. The
additional repository-root Ruff sweep reports existing errors under
`docs/web-tests`; the Python workspace checks pass.

Draft user guidance covers the supporting server requirement, safe
repetition of partial work and whole-batch exhaustion. The guide
sections stay hidden until release. Vale 3.24.0 passed for the added
draft prose; no paired deployed SDK/server retry acceptance was run.
Companion server: https://github.com/lancedb/sophon/pull/9812.

BREAKING CHANGE: Rust callers constructing `FunctionRegistrationRequest`
or `FunctionErrorRecord` with struct literals must supply the new
`retry_policy` or `attempts` field, respectively.

python/src/util.rs

@@ -70,3 +70,14 @@ pub fn parse_field_path(path: &str) -> PyResult<Vec<String>> {
 /// A wrapper around a LanceDB type to allow it to be used in Python
 #[derive(Debug, Clone)]
 pub struct PyLanceDB<T>(pub T);
+/// Validate the Function retry wire contract using the same rules as Rust APIs.
+#[pyo3::pyfunction]
+pub fn validate_function_retry_policy(json: &str) -> pyo3::PyResult<()> {
+    let policy: lancedb::function::FunctionRetryPolicy =
+        serde_json::from_str(json).map_err(|error| {
+            pyo3::exceptions::PyValueError::new_err(format!("invalid retry_policy: {error}"))
+        })?;
+    policy
+        .validate()
+        .map_err(|error| pyo3::exceptions::PyValueError::new_err(error.to_string()))
+}