feat: added limit key counts for memory cache

[0Ams]

When using local memory, it is necessary to limit the max memory of nodejs. We want to limit the number of keys that can be cached for this.

please, check this contents.

thanks :)

[kwhitley]

Happy to merge this, but would love it if you added the feature to the README where appropriate :)

[0Ams]

@kwhitley I added additional information to README. Let me know if there's anything else I need to work on. tx :)

[0Ams]

@kwhitley please give me feedback :)