- Add --path:src and --threads:on to nim.cfg so tests compile without manual flags
- Add tests/config.nims for automatic path resolution in test directory
- Simplify nimble task definitions (remove redundant flags now in nim.cfg)
- Fix Dockerfile.source comment: remove obsolete nimmax reference
This makes 'nim c tests/test_all.nim' and 'nimble test' work out of the box.