feat: resolve latest Function versions (#4949)

## Problem

Function catalog lookup required an exact version string even though
callers
commonly need the latest currently visible immutable revision. On the
current
SDK, resolving that version required an out-of-band catalog query before
calling
`get_function`.

## Change

- Make Python `get_function(name)` default to latest while accepting
`int` or
  `str` for exact lookup.
- Normalize integer versions to their decimal string form and reject
`bool`
  explicitly. Existing string validation and errors remain unchanged.
- Thread `None` through the rebuilt PyO3 binding and route it to the new
Rust
  `Connection::get_function_latest`.
- Resolve latest through the existing catalog `DESCRIBE FUNCTION` path
without
`WITH (version = ...)`. The returned value is one exact immutable
version, not
  a mutable alias.
- Preserve the existing Rust exact-version API.

## Validation

On the designated EC2 host with the rebuilt extension:

- `test_local_function_catalog_operations_are_not_supported`: **1
passed**.
  This crosses the Python connection, rebuilt PyO3, and embedded Rust
  `NotSupported` boundary with the omitted-version call.
- Async and sync catalog-path tests: **2 passed**, 117 deselected.
- Remote SQL Function creation/description integration test: **1
passed**.
- An earlier Rust invocation with the wrong module path matched **0
tests**;
  it is retained as harness evidence and is not counted as a pass.

## Scope

This is the Function lookup SDK slice. It does not include the separate
atomic
rebind/publication server work tracked under ENT-3418.

python/src/connection.rs

@@ -877,22 +877,22 @@ impl Connection {
         })
     }
 
-    #[pyo3(signature = (name, version, namespace_path=None))]
+    #[pyo3(signature = (name, version=None, namespace_path=None))]
     pub fn get_function(
         self_: PyRef<'_, Self>,
         name: String,
-        version: String,
+        version: Option<String>,
         namespace_path: Option<Vec<String>>,
     ) -> PyResult<Bound<'_, PyAny>> {
         let inner = self_.get_inner()?.clone();
         let namespace_path = namespace_path.unwrap_or_default();
         future_into_py(self_.py(), async move {
-            inner
-                .get_function(name, version, &namespace_path)
-                .await
-                .infer_error()?
-                .to_canonical_json()
-                .infer_error()
+            let function = match version {
+                Some(version) => inner.get_function(name, version, &namespace_path).await,
+                None => inner.get_function_latest(name, &namespace_path).await,
+            }
+            .infer_error()?;
+            function.to_canonical_json().infer_error()
         })
     }