Fix sparse search

[maximedb]

Hi,

This pull request fixes two issues with the sparse search:

1. Because of the step in trange, some queries are never evaluated (only the first one of each batch is evaluated) as reported in Error in beir/beir/retrieval/search/sparse/sparse_search.py #60.
2. Dense search skips some results (see here), this was not implemented in the sparse search. It impacts the results on ArguAna and Quora (Can't understand a certain line #37)

Let me know if you have any questions.

Maxime.

[thakur-nandan]

Hi @maximedb and @jin530,

Thanks for the pull request. Indeed as mentioned in #60, this is an error that sadly I wasn't able to find earlier myself.
Nevertheless, the scores for SPARTA reported in the BEIR paper are accurate. It used an old script that did not have the issue. I will soon have a look and merge the PR.

Kind Regards,
Nandan Thakur