[SC-39] Add code coverage reporting for the contracts workspace

[yusuftomilola]

Overview

CI runs cargo test --all but never measures coverage — which is exactly how multisig_transfer reached 755 lines with zero tests unnoticed ([SC-32]).

Tasks

• Add cargo-llvm-cov to CI and generate an lcov report.
• Print a per-crate coverage summary so gaps are visible at a glance.
• Set a workspace threshold at the current measured level so the build stays green, then ratchet upward.
• Add a per-crate floor — this is what catches a zero-coverage crate that a workspace average would hide.
• Optionally upload to Codecov and add a badge.

Acceptance Criteria

• Coverage runs in CI with per-crate numbers.
• A crate with no tests fails the per-crate floor.
• Thresholds are committed and passing.

Dependencies

Pairs with [SC-32], [SC-40], [SC-41].

Notes for Contributors

Requires Rust + Soroban. Workspace: contracts/ (soroban-sdk 22, members: assetsup, contrib, multisig-wallet, multisig_transfer, asset-maintenance). Run cargo test --all, cargo fmt --all -- --check, and cargo clippy --all-targets --all-features -- -D warnings before opening a PR — CI enforces all three. Comment below to be assigned.

[amberly-d]

@amberly-d has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

can i solve this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @amberly-d to this issue.

[drips-wave]

Congratulations, @amberly-d! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @amberly-d: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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