fix(macos): handle device names containing embedded NULs

[malpern]

Summary

• Truncate macOS HID device names at the first embedded NUL before calling device_matches or register_device.
• Use the existing hash fallback, or skip the entry, when the usable name is empty.
• Add regression coverage for valid names, embedded NULs, empty prefixes, and preserving U+FFFD.

Why

karabiner-driverkit converts these names with CString::new(...).expect(...). An embedded NUL therefore panics instead of being handled as a malformed device name, which aborts Kanata and stops remapping. I originally encountered this downstream in malpern/KeyPath#631.

The change is limited to the macOS device-name paths that cross this C string boundary; ordinary names retain their existing matching behavior.

Validation

• cargo fmt --all --check
• cargo test device_name_tests
• cargo test --all
• cargo clippy --all -- -D warnings
• cargo test --all --features=cmd
• cargo clippy --all --features=cmd -- -D warnings