enable mobius in fast tests and align discrepancy smoke CLI flows

[xadupre]

Describe your changes

Fast tests only checked modelbuilder; this PR adds Mobius coverage in the smoke test path.

Addressed review feedback by adding the missing --test argument to the Mobius run invocation in test/cli/test_cli_test_model_smoke.py, aligning it with the documented/tested run flow.

Also addressed follow-up feedback by fusing the common run --config --test --output_path logic used by both modelbuilder and Mobius discrepancy smoke tests into a shared helper to reduce duplication.

Finally, aligned the torch-export discrepancy path with the same command-line flow by switching it to use a CLI run config (with OnnxConversion) and --test, so all discrepancy smoke paths follow a consistent pattern.

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.

(Optional) Issue link

[Copilot]

Pull request overview

This PR updates the CLI smoke/discrepancy test to support multiple “exporters” (model builder, Mobius, torch-export) and to drive discrepancy checks through a consistent olive run --config ... --test ... --output_path ... flow.

Changes:

• Added exporter selection (--exporter) and refactored discrepancy runs into exporter-specific helpers plus a shared run --config --test --output_path helper.
• Added Mobius and torch-export discrepancy run-config generation paths (MobiusBuilder and OnnxConversion respectively).
• Introduced optional Mobius availability detection via importlib.util.find_spec.