Add eval_batch_size argument to cross encoder evaluators

[yunyu]

Cross encoder eval can be very slow, especially if you can fit way bigger batch sizes than the default. This PR allows passing in eval_batch_size to cross encoder evaluators

[fkdosilovic]

This is a useful addition as far as I'm concerned. @yunyu Would you also like to add an option to pass the show_progress_bar argument in the same PR (if @tomaarsen agrees)?

cc @tomaarsen

[tomaarsen]

Apologies for the delay! I would indeed be interested in batch_size and show_progress_bar options for all CE Evaluators.

• Tom Aarsen