Add 500-protein human SwissProt subset for mhcquant SDRF test

[jonasscheid]

Summary

Adds testdata/UP000005640_9606_500prot.fasta, a 500-protein subset of the human SwissProt proteome (UP000005640), for use as the default FASTA in the upcoming test_sdrf profile in nf-core/mhcquant.

Rationale

The current full proteome (UP000005640_9606.fasta, 20,610 proteins) causes the CometAdapter step in the SDRF test to exceed the 6 GB CI memory cap or hit the 2 h wall-time when combined with unspecific cleavage on the PXD009752 test RAW files.

Benchmarking showed the 500-protein subset:

• Reduces CometAdapter wall-time from ~35 min to ~3 min per file (at spectrum_batch_size=20000)
• Keeps peak RSS within the 6 GB cap
• Still yields ~100 peptides at q<0.01 FDR, giving Percolator enough targets to train a stable SVM

Content

• First 500 entries of UP000005640_9606.fasta (deterministic head)
• 329 KB (vs 13.6 MB for the full proteome)

Related

Used by nf-core/mhcquant#445 (SDRF/PRIDE input support).