docs: publish the Function pages only once Functions launch

The two Function pages declare `launch: functions`, and every other page
marks what it says about Functions, so the assembled site leaves them out
until the launch. Before it, the pages that offered Functions for Python
work point Enterprise readers at Geneva instead.

The SQL Function example now uses Arrow type names, which the server
requires, and states the 3.12 default for `python_version`.

docs/web/feature-engineering/data-evolution.mdx

@@ -108,10 +108,17 @@ exist when that does not fit:
 - A [computed column](/feature-engineering/add-computed-column) declares the
   expression and leaves the column empty, so you choose when the work happens.
   That is the right default on a large table.
+{/* if functions launched */}
 - A [function](/management/function) fills a column with Python, for values SQL
   cannot express -- an embedding, a model call, an image decode.
+{/* end if */}
+{/* if functions not launched */}
+- On LanceDB Enterprise, [Geneva](/geneva) fills a column with Python, for
+  values SQL cannot express -- an embedding, a model call, an image decode.
+{/* end if */}
 
-On a deployment, both have to be enabled there.
+A deployment has to enable computed columns before you use them.
+Functions need enabling there too. {/* if functions launched */}
 
 ## What to read next {#next}