Add full balance-flow test coverage for release_funds in tests/lifecycle.rs

[1nonlypiece]

📌 Description

COVERAGE_ANALYSIS.md reports 92.16% line coverage with the event-publish lines
in release_funds showing as uncovered, and the integration suite in
tests/lifecycle.rs only loosely asserts the escrow balance movement. We need
explicit balance-delta assertions proving that on release_funds the
contract address is debited and success_destination is credited by exactly
vault.amount.

Goal: add focused tests asserting the exact USDC balance changes of the
contract, creator, and success_destination across every release_funds path.

🎯 Requirements and Context

• Must be deterministic and isolated.
• Cover both release triggers: validated-before-deadline and deadline-reached.
• Assert pre/post balances on the contract address and success_destination.
• Confirm the funds_released event is emitted with the correct amount via
  env.events().

🛠️ Suggested Execution

1. Fork the repo and create a branch

git checkout -b feature/release-funds-balance-tests

2. Implement changes

• Tests: extend tests/lifecycle.rs with balance-delta assertions using
  TokenClient::balance before/after release_funds.
• Assert the funds_released event with env.events().all().
• Docs: update TESTING_GUIDE.md and COVERAGE_ANALYSIS.md with the new cases.
• Add comments explaining each balance assertion.

3. Test and commit

• Run cargo test and regenerate coverage with the tarpaulin.toml config.
• Cover edge cases: validated release, deadline release, contract balance reaches
  zero post-release, double-release rejection leaves balances unchanged.

Example commit message

test: explicit balance-flow coverage for release_funds in lifecycle suite

✅ Guidelines

• Minimum 95% test coverage on release_funds lines.
• Clear documentation of the new cases in TESTING_GUIDE.md.
• All tests deterministic and passing.
• Timeframe: 96 hours.

🏷️ Labels

type-testing · area-contracts · MAYBE REWARDED · GRANTFOX OSS ·
OFFICIAL CAMPAIGN

💬 Community & Support

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• Please introduce yourself before you start so we can avoid duplicate work,
  pair you with a reviewer, and merge your PR quickly.