ci: publish per-package rustdoc

[maxw06]

Closes #1481

Summary

• Add a Rustdoc workflow that runs cargo doc -p quicklendx-contracts --no-deps for the contract package.
• Upload generated rustdoc as an artifact for PR review and publish it to GitHub Pages on pushes to main.
• Link the rustdoc runbook from the README and document the local command / published layout in docs/RUSTDOC.md.
• Fix existing rustdoc compile blockers so the new job can actually complete: declare the existing address_summary and idempotency modules, add the missing idempotency imports, and collapse duplicated compute_yield definitions into one compatible implementation.

Validation

• cargo doc -p quicklendx-contracts --no-deps passes and generates target/doc/quicklendx_contracts/index.html.
• git diff --check passes.
• cargo fmt is currently blocked by a pre-existing parse error in quicklendx-contracts/src/test_bid_capacity_stress.rs (unexpected closing delimiter); no formatter churn is included in this PR.

[Baskarayelu]

thanks for the contribution! our workflow only merges a PR when its author is assigned to the linked issue — please get assigned to an open issue first, then raise the PR. closing as invalid for now 🙏