feat: migrate from Docker to pixi for BtToxin_Digger execution

- Add pixi.toml with digger and pipeline environments
- Implement PixiRunner class replacing DockerContainerManager
- Add run_digger_stage.py for standalone digger execution
- Update run_single_fna_pipeline.py to use PixiRunner
- Remove docker dependency from pyproject.toml
- Delete docker_client.py (no longer needed)

BREAKING CHANGE: Docker is no longer required. Use 'pixi install' instead.

pyproject.toml

@@ -13,7 +13,6 @@ dependencies = [
     "pandas>=2.0.0",
     "matplotlib>=3.7.0",
     "seaborn>=0.12.2; python_version>='3.9'",
-    "docker>=6.1.0",
 ]
 
 [project.scripts]