Added unit and integration tests for the Wrap widget

#400 in iced-rs/iced_aw — merged 2026-01-02

Summary of Changes

• Integration tests (tests/wrap_integration_tests.rs)
• Unit tests (src/widget/wrap.rs):
• Tests both horizontal and vertical Wrap variants
• Snapshot tests for visual regression

cargo test --lib wrap::tests && cargo test --test wrap_integration_tests