Update model package cli to match latest schema

[xiaoyu-work]

Describe your changes

Update model package cli to match latest schema

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 olive generate-model-package to emit an ORT model-package “proposal-shaped” directory layout and schema, and expands test coverage to validate the new manifest/metadata/variant format and external-data handling.

Changes:

• Reworked CLI packaging to generate manifest.json with schema_version/components, and per-component metadata.json + per-variant variant.json under top-level component directories (no models/ wrapper).
• Added a write_model_package writer with validation, configs/ copying, and optional cross-variant external-data dedup into shared_weights/.
• Greatly expanded CLI+writer tests (single-source allowed, composite inference precedence, compatibility parsing, dedup behavior, and safety checks).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
olive/cli/model_package.py	Refactors the CLI to build VariantSpecs and writes a proposal-shaped model package (manifest/metadata/variant.json), including external-data discovery and optional dedup.
test/cli/test_model_package.py	Replaces/extends tests to validate the new schema/layout, helper behavior, composite inference precedence, and external-data dedup + safety.