How to properly embed the cache in an already finished system?

Question

go

Hello. I made a website. There are currently two packages.
This is a site which, roughly speaking, is a set of functions due to how the site works
and the public package which has a web server in it, etc. in the functions of this package, the data is received and processed, which are transferred to the site package, and the data that comes from the site functions is processed.
Now we need to add the cache.
I have three options in my head
: 1. embed the cache in the functions of the public package
2. embed the cache in the functions of the site package
3. Make a cache layer and get the site ->cache ->public architecture where site,cache and public are different packages.
Which option would be better? If you have a better version than mine, please let me know :)