Speed up short reads filtering by processing multiple records together

[imartayan]

Hey @bede!

This PR aims to speed up short reads filtering by packing multiple records until we reach a length threshold (currently 8000 bp) and processing this batch with a single call to simd_minimizers. It introduces a RecordBuffer type that packs multiples sequences and headers in a single Vec<u8>, and uses this type internally in FilterProcessor to batch the operations. Currently, it is only implemented for the ParallelProcessor trait and isn't used for paired reads yet.

This might use a bit more copy than before since we have to keep some records longer (thus slightly slowing down long reads processing) but should bring a significant speedup for short reads.

Let me know if you're happy with the new performances and if you get consistent results with the previous implementation. If so, I can adapt the code to support paired reads as well.

Best,
Igor

[bede]

Many thanks @imartayan!
Results look great at a glance. For the uncompressed fastq R1 reads (forward reads only) of the 2x150bp simulated reads for rsviruses17900, this PR increases throughput from 300Mbp/s to 542Mbp/s on my local M1 machine. For fastq.gz, throughput remains capped at ~190Mbp/s (though as discussed we hopefully can 2x in the future with parallel readers). This approach would also deliver improvements in conjunction with faster compression approaches, and binary formats like uBAM (#33) and vbq (#31) that may be supported in future.

[bede]

Hi Igor,
I'm sorry for not responding here yet; first impressions are really good. I'll get back to you after a closer look.

Thanks,
Bede