refactor: replace mea with asyncband 0.7.1

[tisonkun]

Summary

• replace mea::mutex::Mutex with asyncband::mutex::Mutex from AsyncBand 0.7.1
• enable only AsyncBand's mutex feature
• raise the workspace MSRV to Rust 1.86, matching AsyncBand 0.7.1
• require 0.7.1 because AsyncBand 0.7.0 has been yanked

Testing

• cargo fmt --all -- --check
• cargo check --workspace --all-features
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --no-fail-fast
• cargo test --doc --all-features --workspace