RCWA Grating Example

### 📝 Description of the example

How to set up geometry and extract results from an RCWA grating simulation. This will be a prerequisite for more advanced workflows, for example https://optics.ansys.com/hc/en-us/articles/33794233218579-RGB-Augmented-Reality-Optical-System.

### 📁 Files needed for running the example

No files needed

### 💻 Which operating system are you using?

Windows

### 📀 Which ANSYS version are you using?

2026 R1

### 🐍 Which Python version are you using?

3.9

### 📦 Installed packages

```shell
matplotlib-inline==0.2.1
```

The issue does not name a target file, test, or entry point; begin by reviewing the open linked pull request #139 and the repository's existing example structure. Done should include a runnable RCWA grating example that demonstrates geometry setup and result extraction for the stated environment.

Written by the indexing model from the issue text.