Add clear volume mesh

### 📝 Description of the feature

API's to clear volume mesh on cell zonelets and topo volumes

### 💡 Steps for implementing the feature

_No response_

### 🔗 Useful links and references

_No response_

Start by locating the API definitions for cell zonelets and topo volumes and determine the expected behavior of clearing their volume mesh. The issue does not name files, tests, or acceptance criteria; confirm the API shape and define completion as both object types supporting the requested clear operation with documented verification.

Written by the indexing model from the issue text.