The grammar should return clean objects

Currently the grammar yields linkml instances like:

```python
NodeRename(id='CHANGE:001', type='NodeRename', ...,` old_value=Token('SINGLE_QUOTE_LITERAL', "'nuclear envelope'"), new_value=Token('SINGLE_QUOTE_LITERAL', "'foo bar'")`
```

No need for this

Also the rendered json is:

```json
{
"id": "CHANGE:001",
"type": "NodeRename",
"old_value": "'nuclear envelope'",
"new_value": "'foo bar'",
"about_node": "GO:0005635",
"about_node_representation": "curie",
"@type": "NodeRename"
}
```

The single quotes are not necessary. It's already a string field.

Currently downstream code such as OAK has a workaround for this:

https://github.com/INCATools/ontology-access-kit/blob/8da76e19698058b43c4ae4ba2b5bcda35a1c851a/src/oaklib/utilities/kgcl_utilities.py#L99-L123

In theory this should still work with clean code but we should still wait until 1.0.0

Locate the Python grammar or parser entry point that creates the shown LinkML NodeRename instance, then reproduce the example. Use the OAK workaround linked in the issue as a compatibility reference and verify that parsed values and rendered JSON no longer contain Token wrappers or unnecessary quote characters.

Written by the indexing model from the issue text.