Refactor Clip and OpenAi query encoders

[lintool]

Other minor tweaks/fixes along the way

[lintool]

@MXueguang @jasper-xian @justram I think this is ready, I've run the following:

nohup python -m pyserini.2cr.atomic --all --directory runs/ --display-commands >& logs/log.atomic &

nohup python -m pyserini.2cr.msmarco --collection v1-passage --condition openai-ada2 --directory runs/ --display-commands >& logs/log.openai-ada2 &
nohup python -m pyserini.2cr.msmarco --collection v1-passage --condition openai-ada2-hyde --directory runs/ --display-commands >& logs/log.openai-ada2-hyde &
nohup python -m pyserini.2cr.msmarco --collection v1-passage --condition openai-text-embedding-3-large --directory runs/ --display-commands >& logs/log.openai-text-embedding-3-large &

The OpenAI runs were successful.
The AToMiC run gives the same result as #2015