Plotting mesh using PyMechanical

### 📝 Description of the feature

Hi Team,
As we using app.plot() to visualize the 3D Geometry, Need same functionality for plotting mesh & post processing.

### 💡 Steps for implementing the feature

_No response_

### 🔗 Useful links and references

_No response_

Start by examining the existing app.plot() functionality referenced in the issue and how PyMechanical represents geometry and mesh data. The issue provides no files, tests, implementation steps, or acceptance criteria; the work is complete only when mesh and post-processing results can be plotted with comparable functionality.

Written by the indexing model from the issue text.