Initial columns functions

[lauradmartens]

Fixes #9 when finished and partly #6 for discoverability of columns

[lauradmartens]

• We might have to add a hierarchy to the column names because multiple tables contain same column names

[codecov-commenter]

Codecov Report

Merging #22 (484af92) into main (0acfba3) will increase coverage by 2.05%. The diff coverage is 90.47%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #22 +/- ## ========================================== + Coverage 88.40% 90.45% +2.05% ========================================== Files 6 6 Lines 138 241 +103 ========================================== + Hits 122 218 +96 - Misses 16 23 +7 ``` | [Impacted Files](https://codecov.io/gh/scverse/genomic-features/pull/22?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse) | Coverage Δ | | |---|---|---| | [src/genomic\_features/\_core/filters.py](https://codecov.io/gh/scverse/genomic-features/pull/22?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse#diff-c3JjL2dlbm9taWNfZmVhdHVyZXMvX2NvcmUvZmlsdGVycy5weQ==) | `89.47% <ø> (+3.94%)` | :arrow_up: | | [src/genomic\_features/ensembl/ensembldb.py](https://codecov.io/gh/scverse/genomic-features/pull/22?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scverse#diff-c3JjL2dlbm9taWNfZmVhdHVyZXMvZW5zZW1ibC9lbnNlbWJsZGIucHk=) | `90.25% <90.47%> (+0.06%)` | :arrow_up: |

[lauradmartens]

• Check why inner join tb1.left_join(tb2, 'gene_id').execute() returns one column called gene_id while left join returns gene_id_x and gene_id_y

[lauradmartens]

This test needs to be checked: https://github.com/scverse/genomic-features/blob/45d97ac1d586c7c11bfa54afb8e1445ef1e5cab6/tests/test_columns.py#L79