examples: update UDT parsing example to be in line with docs

[sylwiaszunejko]

What's done

Previously there was some discrepancy between the examples, specifically how to parse a row into a custom type and and the docs about UDT.

Now it is updated.

Fixes: #829

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• I have provided docstrings for the public items that I want to introduce.
• I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.

[sylwiaszunejko]

CI fails due to: #847

[piodul]

#847 was fixed, please rebase.

[sylwiaszunejko]

#847 was fixed, please rebase.

Done