Improve form performance (tracking issue)

### What should we do?

We should conduct an optimization pass for fjs, as there are some performance issues reported when dealing with large forms.

### Why should we do it?

To keep the modeling experience as fluid as possible.

Sample form available [here](https://forum.camunda.io/t/camunda-modeler-with-large-form/48076).

### Potential improvements

#### To research

- [ ] can we improve the evaluation time of FEEL ?
- [ ] can we efficiently cache the result of FEEL evaluation, and if so, would performance improve ?
- [ ] can we reduce the overall number of re-renders by using signals ?

#### To implement

- [x] minimize the number of recalculations of the feel data context (shipped via #808)
- [x] https://github.com/bpmn-io/form-js/issues/958

Start with the linked large-form sample and review the remaining unchecked questions around FEEL evaluation, caching evaluation results, and reducing re-renders with signals. Check the completed work in #808 and #958 to avoid duplicating it. Done means identifying and implementing measurable improvements for large forms, with performance results recorded.

Written by the indexing model from the issue text.