BBsplit unmapped - enhancement

[EladH1]

PR checklist

Closes #XXX

• This comment contains a description of changes (with reason).

As this is in some cases the first alignment it's beneficial to have also unaligned fastq saved.

• If you've fixed a bug or added code that should be tested, add tests!
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    • nf-core modules test <MODULE> --profile docker
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    • nf-core subworkflows test <SUBWORKFLOW> --profile docker
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[EladH1]

The issue was not resolved as unmapped output non-deterministic result.
so every --update-snapshot generate new md5sum.