Integration tests: vault → pool/settlement flow with mock USDC

[greatest0fallt1me]

Description

Add a Soroban test harness that exercises multi-contract flows (as applicable to current architecture) using a mock token, asserting balances and key events across calls.

Requirements and context

• Prefer a dedicated integration test module or crate if it keeps lib.rs lean.
• Document how to run it in README.md.

Suggested execution

• Fork the repo and create a branch: git checkout -b test/integration-vault-settlement
• Implement changes in the Callora-Contracts Soroban workspace (contracts/*/src/).
• Run cargo fmt, cargo clippy --all-targets --all-features -- -D warnings, and cargo test from the workspace root.
• For WASM release builds: cargo build --target wasm32-unknown-unknown --release -p callora-vault (adjust -p if the crate name differs).

Deliverables

• Tests under workspace + minimal doc updates.
• Security notes: what assumptions the mock makes vs mainnet USDC.

Test and commit

• Run tests and ./scripts/coverage.sh (or cargo tarpaulin per tarpaulin.toml).
• Cover edge cases; include summarized test output and brief security notes in the PR description.

Example commit message

test: cross-contract vault and settlement flow

Guidelines

• Minimum 95% line coverage for touched crates (workspace policy).
• Clear documentation (Rust /// on public items where applicable; repo markdown as needed).
• Timeframe: 96 hours from assignment unless agreed otherwise.

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[Ebuka321]

@Ebuka321 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hello Good day. Please can i work on these ?

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