* [Feature](Variant) Implement variant new sub column access method
The query SELECT v["a"]["b"] from simple_var WHERE cast(v["a"]["b"] as int) = 1 encompasses three primary testing scenarios:
```
1. A basic test involving the variant data type.
2. A scenario dealing with GitHub event data in the context of a variant.
3. A case related to the TPC-H benchmark using a variant.
```
