Columns should be namespaced (e.g. under `_columns`)

> Note: For convenience, we automatically map the database "columns" (aka properties), based on the schema defined in the Collection, into getter/setter attributes on the CollectionRowBlock instances.

This should be namespaced to avoid clashing with class members. E.g. in the following the column `remove` clashes with the method `remove`:

```python
In [84]: row.remove # this returns a method, not the column (see below)
Out[84]: >

In [85]: coll.get()
Out[85]:
{'id': 'be92dd44-...-c77316403c58',
'version': 28,
'name': [['Labels per repo']],
'schema': {'"-z;': {'name': 'remove', 'type': 'text'}, # here's the `remove` column
'Pq($': {'name': 'Description', 'type': 'text'},
'S0=w': {'name': 'Color', 'type': 'text'},
'u&]8': {'name': 'Repository',
'type': 'relation',
'property': '/lVl',
'collection_id': '60f1e59a-...-9b030f1b9c4b'},
'title': {'name': 'Label', 'type': 'title'}},
'format': {'collection_page_properties': [{'visible': True,
'property': 'Pq($'},
{'visible': True, 'property': 'S0=w'}]},
'parent_id': 'cb6fb9a3-...-b77de1bb8ed7',
'parent_table': 'block',
'alive': True}

In [86]: row.repository # this returns a cell value
Out[86]:
[,
]
```

Start by locating the CollectionRowBlock logic that maps schema columns into getter/setter attributes, using the reported `remove` and `repository` examples as references. Done means column values are available under a namespace such as `_columns` without clashing with CollectionRowBlock methods, while existing column access behavior is covered by tests.

Written by the indexing model from the issue text.