fix: multiple unused variables in test.rs cause Clippy CI failure

[Pvsaint]

Problem

test.rs has numerous unused variable warnings that block CI under -D warnings:

warning: unused variable: `env`         --> test.rs:12
warning: unused variable: `expires_at`  --> test.rs:87, 114, 331, 672
warning: unused variable: `currency`    --> test.rs:112, 329, 670
warning: unused variable: `deposit_address` --> test.rs:113, 330, 671

These typically arise from test setup code where variables are declared but the test was later refactored to not use them.

Acceptance Criteria

• All listed unused variables are either prefixed with _ (e.g. _env) or removed if genuinely unnecessary
• Prefer removal over prefixing where the variable serves no purpose
• cargo clippy --all-targets --all-features -- -D warnings passes for test.rs

Branch & Commit Examples

branch: fix/clippy-warnings-cleanup
commit: fix(tests): prefix or remove unused variables in test.rs