fix(release): publish missing Rust crate version

[Iktahana]

Summary

• replace the unreliable local cargo info existence check with the crates.io version API
• distinguish published (HTTP 200), missing (HTTP 404), and unexpected registry responses
• allow the pending mdi-core@2.0.3 release to publish and tag correctly

Verification

• registry endpoint returns HTTP 404 for mdi-core@2.0.3
• workflow diff passes git diff --check
• prior crate package verification and full PR suite passed in fix(core): conform platform exports to official contracts #54

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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