Added testing coverage for the TabBar widget

#393 in iced-rs/iced_aw — merged 2025-12-31

Summary of Key Changes

Modified src/widget/tab_bar.rs

• Implemented operate() method to support widget testing and interaction
• added unit tests

Added tests/tab_bar_integration_tests.rs

# tab bar tests
cargo test --lib tab_bar && cargo test --test tab_bar_integration_tests

# all tests
cargo test --lib --tests --bins