Tests for context_menu, custom_layout, date_picker

#374 in iced-rs/iced_aw — merged 2025-12-26

# Unit tests
cargo test --lib widget::context_menu
cargo test --lib widget::custom_layout
cargo test --lib widget::date_picker

# Integration tests
cargo test --test context_menu_integration_tests
cargo test --test custom_layout_integration_tests
cargo test --test date_picker_integration_tests