Qualified function calls result in "Function not found"

When I parse this query with SqlAnalyzer::analyzeNextStatement, it succeeds:
```sql
CREATE FUNCTION foo.bar.baz() AS (1); SELECT baz();
```

But this query fails:

```sql
CREATE FUNCTION foo.bar.baz() AS (1); SELECT foo.bar.baz();
```

It looks like singleton and non-singleton paths are handled differently, and non-singleton paths don't work.

https://github.com/google/zetasql/blob/3e5d33d707919df42d1083665113ef05dd78ffff/zetasql/public/catalog.cc#L120-L128

Start with zetasql/public/catalog.cc at the linked lines and trace how SqlAnalyzer::analyzeNextStatement resolves singleton versus non-singleton function paths. Reproduce the two CREATE FUNCTION and SELECT queries, then verify that the qualified call foo.bar.baz() resolves successfully like the unqualified baz() call.

Written by the indexing model from the issue text.