fix: split-duckdb-index error when indexing columns with spaces
After deploying split-duckdb-index, there are some errors because of column names with spaces like:
```
duckdb.BinderException: Binder Error: Referenced column "Mean" not found in FROM clause!
Candidate bindings: "read_parquet.Model"
LINE 1: ...f_index_id, Ranking,User,Model,Results,**Mean Reward**,Std Reward FROM read_parque...
    
                                          ^
```    
This PR fixes this error.
fix: split-duckdb-index error when indexing columns with spaces: After deploying split-duckdb-index, there are some errors because of column names with spaces like:
```
duckdb.BinderException: Binder Error: Referenced column "Mean" not found in FROM clause!
Candidate bindings: "read_parquet.Model"
LINE 1: ...f_index_id, Ranking,User,Model,Results,**Mean Reward**,Std Reward FROM read_parque...
    
                                          ^
```    
This PR fixes this error.