Fix conda slug and full path resolution

[mrDzurb]

Summary

Fixes conda environment resolution so service conda lookup is only used for short slug inputs, while full oci://... paths are handled directly.

Changes

• Route full OCI conda paths through EnvInfo.from_path() without reading service_pack/index.json.
• Validate full OCI conda paths directly and return path-specific errors.
• Keep valid service conda slug resolution unchanged.
• Return clearer errors when:
  • the service conda list cannot be extracted
  • a provided slug is not a service conda slug
• Preserve custom published conda paths as published.
• Pass auth through full-path resolution.
• Add regression coverage for slug failures and full-path routing.

Validation

• tests/unitary/with_extras/model/test_env_info.py -q: 24 passed
• python -m py_compile on changed files: passed
• git diff --check: passed

Notes

test_artifact.py could not be collected in the local venv because skl2onnx is not installed, but the changed file compiles cleanly.

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