productive_only option in filter_bcr

[zktuong]

Currently productive_only option is toggled at the beginning of filter_contigs to restrict analysis.

However, during productive_only = False, because there's more contigs to screen against, you might end up with lesser contigs that pass the filter.

Ideally, the function should still prioritise productive contigs over non-productive contigs but right now it just keeps contigs based on UMI when productive_only = False. Perhaps a simple if-else statement might be useful to do this before comparing UMI?

However, I'm not sure what happens if there's more than 1 productive contigs of the same locus - would this impact on subsequent steps?