[Bug]: appdirs is officialy deprecated; please replace by platformdirs

### Component

Installation

### Severity

P2 - Medium (workaround exists)

### Shiny Version

1.4.0

### Python Version

3.12.11

### Minimal Reproducible Example

```python
`pip install shiny` installs `appdirs` as dependency
```

### Behavior

`pip install shiny` installs `platformdirs` as dependency

### Error Messages (if any)

```shell

```

### Environment

```markdown
rockylinux 8
```