ci: enforce rustdoc warnings and test workspace

[darcszn]

Summary

• Add a workspace-wide cargo test --locked --workspace job alongside the existing per-package contract tests.
• Require both package-level and workspace-wide test jobs to pass before the WASM build runs.
• Keep the existing rustdoc warning enforcement: the docs job already sets RUSTDOCFLAGS: -D warnings for cargo doc.

Checklist

• cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings and cargo test --workspace pass (not run as requested)
• New behaviour is covered by tests (including the unauthorised / error path) (CI-only change; no runtime behaviour changed)
• docs/CONTRACTS.md and rustdoc updated for any interface, storage, event or error change (not applicable; no interface changes)
• Error codes were appended, not renumbered (not applicable; no error codes changed)

Validation: Tests and CI checks were not run, and dependencies were not installed, as requested.

closes #118
closes #119

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