deepretro.utils.az mis-handles absolute and unset config paths

[shreyasvinaya]

Summary

deepretro.utils.az builds config paths with raw string concatenation against the repo root:

AZ_MODEL_CONFIG_PATH = f"{root_dir}/{os.getenv('AZ_MODEL_CONFIG_PATH')}"
AZ_MODELS_PATH = f"{root_dir}/{os.getenv('AZ_MODELS_PATH')}"

Affected code

• deepretro/utils/az.py

Problems

1. Absolute env-var paths are mangled.
   • If AZ_MODEL_CONFIG_PATH=/tmp/config.yml, the effective path becomes <repo-root>//tmp/config.yml.
2. Unset env vars become literal .../None paths.
3. The path handling is inconsistent with normal user expectations for environment-provided file paths.

Why this matters

This makes valid external configurations fail unexpectedly, especially in CI, notebooks, or shared environments where configs live outside the repo.

Expected behavior

• Absolute env-var paths should be used as-is.
• Relative env-var paths can optionally be resolved against the project root.
• Missing env vars should stay missing and trigger a clear error later, not silently turn into .../None.

Suggested direction

Use Path-based resolution with explicit handling for:

• unset values
• absolute paths
• relative paths