Move unsync and experimental dash caches to a new crate called mini-moka

[tatsuya6502]

This PR marks unsync cache deprecated and completely removes experimental dash cache from moka crate. They have been moved to a new crate called mini-moka.

Reasons

dash cache

• An experimental dash cache was added to moka at v0.8.0.
  • It was an alternative implementation to sync cache.
  • At the time, sync cache had an issue Segmentation faults in moka-cht under heavy workloads on a many-core machine #34.
  • That issue was resolved at v0.9.2.
• dash cache has a smaller but duplicate feature set to sync cache.
  • Now the issue was resolved, there are not many reasons to keep dash cache in moka crate.
• However, there are some users who are happy with dash cash as it provides a smaller but enough feature set for their use cases.
  • So instead of removing dash cache, it would be nice if we move it to a new crate mini-moka that will provide simpler and lighter cache implementations.

unsync cache

• unsync cache seems not popular and has a smaller feature set to sync and future cache.
  • If we move dash cache to mini-moka, it would make sense to move unsync cache to mini-moka too.

Why removing dash cache right now from moka while keeping unsync cache as deprecated?

• dash cache shares some base modules with sync and future caches.

  • Since dash provides different (smaller) feature set than others, it is becoming difficult to maintain the base modules.
  • So removing it now will make the maintenance and development woks much easier.

• If moka user enables dash feature, it will fail to compile and show a message to introduce mini-moka crate.

• On the other hand, unsync cache shares very little part of the base modules with other caches.

  • It is not making maintenance problems now.

• Also, unsync cache is always enabled, and there is no crate feature like dash for it.

  • Thus, there is no way to show the message to introduce mini-moka crate if we completely remove it from moka.
  • So for now, we only mark it deprecated, and make the deprecation warning to introduce mini-moka crate.
  • We will remove unsync cache later at v0.11.0.

[tatsuya6502]

Merging.