test: cover redirect rejection after completed vault

[silentgeckoaudit3801]

Fixes #322.

Adds a lifecycle regression test that completes a vault through release_funds, then verifies redirect_funds rejects the terminal Completed state with Error::VaultNotActive.

Validation: static API inspection only in this environment; I did not run the Soroban/Rust toolchain locally to avoid dependency/toolchain execution here.

[silentgeckoaudit3801]

CI note: cargo fmt --check is now passing after commit 49819c5. The remaining Build, Test & Lint and coverage failures happen before this crate's tests compile, while building dependency ethnum v1.5.2 with Rust 1.97.1 (error[E0512] in ethnum/src/error.rs:16).\n\nI did not change Cargo.lock or pin dependencies here because this PR is intended to stay scoped to the #322 lifecycle regression test.

[1nonlypiece]

@silentgeckoaudit3801 this PR needs to be linked to an issue you're actually assigned to before it can be merged through the campaign — closing for now, happy to take another look once that's in place.