Additional Notices for Moka

The majority of the Moka library is dual-licensed under the MIT and Apache 2.0
licenses.

However, the following files are an exception and are licensed solely under
the Apache License 2.0:

- src/common/frequency_sketch.rs
- src/common/timer_wheel.rs

These files were ported from the Java Caffeine library and are not dual-licensed.

Please refer to the LICENSE-APACHE file for more details on the Apache License 2.0.