Make sure suggested FEEL functions can be executed in forms

[barmac]

What should we do?

• Make sure all suggested functions can be evaluated (finish feat: implement round functions nikku/feelin#79)
• Establish a continuous test for suggested functions

We may need to provide Camunda extensions via a wrapper, or stop suggesting Camunda extensions in forms as they'd need to be provided separately.

Why should we do it?

Problem reported via https://camunda.slack.com/archives/C0693F1NFK5/p1728639145792559
Follow-up discussion https://camunda.slack.com/archives/GP70M0J6M/p1728641414950129