test(escrow): add test for double initialize

[K1NGD4VID]

Summary

Adds a negative test that pins the current AlreadyInitialized behaviour when EscrowContract::initialize is called a second time.

Changes

• contracts/escrow/src/test.rs: new test_initialize_twice_panics test using #[should_panic(expected = "Error(Contract, #1)")], matching the existing #[should_panic] style used elsewhere in the file.

Notes

Local cargo test could not be run on the Windows worktree (dlltool.exe not found); relying on CI (build-and-test) as the gate.

Closes #250