Add CI and unit tests for Python utilities

[philippmuench]

Summary

• Add GitHub Actions workflows: smoke test (syntax + Nextflow) and unit tests (pytest + coverage)
• Add 247 unit tests across 13 test files covering core Python utilities
• Add CI status badges to README
• Improve README with quick start guide, parameter reference, and project structure

Test coverage includes

• Community distribution generation (lognormal, timeseries, replicates, differential)
• CIGAR string parsing and generation (NanoSim, WGSIM, MAF converter)
• NCBI taxonomy building and lineage resolution
• Gold standard file format I/O and read/contig mapping
• Sequence anonymization
• Gene abundance distributions (metatranscriptomic)
• Strain simulation distributions
• Config v1→v2 conversion

Test plan

• Both CI badges show green (smoke test + unit tests)
• Review test output for coverage percentage