replace test files with small synthetic ones

- replaces existing larger libraries and annotations in test cases `test_create_dag_chart` and `test_integration_workflow`
- adds the following new test files:
  - `chr1-10000-20000.fa`: artificial chromosome of length 10'000 (based on human chromosome 1)
  - `chr1-10000-20000.gtf`: matching gene annotation file with two gene and three multi-exon transcripts entries
  - `chr1-10000-20000.transcripts.fa`: sequences of the transcripts listed in the gene annotation file
  - `synthetic.mate_?.fastq.gz`: 10 read pairs randomly sampled from the genic regions of the artificial chromosome
  - `synthetic.*.bed`: BED files with expected alignments for each read; names of overlapping genes are specified in a 7th column
- updates file paths in the relevant sample tables
- extends and updates checksum checking of result files in CI/CD pipeline