Add max refinement elements property for HFSSSettingsOptions

### 📝 Description of the feature

HFSSSettingsOptions has properties for max refinement like use_max_refinement and max_refinement_per_pass, but does not expose the number of max refinement elements, which we would like to set/get.

### 💡 Steps for implementing the feature

_No response_

### 🔗 Useful links and references

Read HFSSSettingsOptions and its existing max-refinement properties first; trace their accessors to the underlying HFSS settings representation. Locate the tests for analogous options, then verify that the max-refinement-elements value can be set and retrieved consistently with the existing properties.

Written by the indexing model from the issue text.