Make long line wrapping optional

Currently very long lines are wrapped, at a certain length.
This introduces many changes in our repo (300+).

Here is an example:

```py
>>> to_yaml_string({'test': 'This is a very very very very very very very very very very very very very very very very long line.'})
'test: This is a very very very very very very very very very very very very very very\n very very long line.\n'
```

I guess it is due to the used ruamel.yaml...
In https://github.com/jlevy/frontmatter-format/blob/main/src/frontmatter_format/yaml_util.py#L66-L67

```py
yaml.width = <...>
```

can e.g. be set.