Formatter parentheses support for `IpyEscapeCommand` (#8207)
## Summary
This PR removes the `todo!()` around `IpyEscapeCommand` in the
formatter.
The `NeedsParentheses` trait needs to be implemented which always return
`Never`. The reason being that if an escape command is parenthesized,
then that's not parsed as an escape command. IOW, the parentheses
shouldn't be present around an escape command.
In the similar way, the `CanSkipOptionalParenthesesVisitor` will skip
this node.
## Test Plan
Updated the `unformatted.ipynb` fixture with new cells containing
IPython escape commands and the corresponding snapshot was verified.
Also, tested it out in a few open source repositories containing
notebooks (`openai/openai-cookbook`, `huggingface/notebooks`).
#### New cells in `unformatted.ipynb`
**Cell 2**
```markdown
A markdown cell
```
**Cell 3**
```python
def some_function(foo, bar):
pass
%matplotlib inline
```
**Cell 4**
```python
foo = %pwd
def some_function(foo,bar,):
foo = %pwd
print(foo
)
```
fixes: #8204
