[PLATI-1363] Use Identity as the default compressor & serializer

[felixmo]

Changes in Rails 7.1 prevent us from passing these in from platform so this change adds the Identity serializer/compressor and makes it the default.

[naveg]

Dalli's pattern seems to be omitting the shared module prefix.

Suggested change

	:compressor => (defined?($TESTING) && $TESTING) ? Compressor : Dalli::Identity,
	:compressor => (defined?($TESTING) && $TESTING) ? Compressor : Identity,

[naveg]

We should arguably update the tests to pass Compressor instead of use the default, if they fail otherwise. I don't feel particularly strongly about that though.

[felixmo]

I tried that initially but it required a good amount of changes. I think we should probably keep the number of changes to a minimum to avoid diverging from upstream too much. Also I think doing it this way will allow us to bring in changes from upstream more easily in the future.

[jasonpenny]

Changes in Rails 7.1 prevent us from passing these in from platform so this change adds the Identity serializer/compressor and makes it the default.

Can you explain more about this?

I would rather stop the bleeding (more and more changes to our fork diverging from upstream). I have to imagine that the newer version of dalli works with newer Rails and does not have an Identify compressor nor serializer.

[felixmo]

@jasonpenny We currently use ZstdSerializer as the :coder to handle both serialization and compression.

Dalli, by default, also uses its own serializer & compressor. I think to avoid serializing & compressing entries twice we've been passing in Identity to override the default :serializer & :compressor.

But as of Rails 7.1, we can only specify either a :coder or (:serializer & :compressor) but not both: https://api.rubyonrails.org/v7.1/classes/ActiveSupport/Cache/Store.html#method-c-new (see description for :coder)

cc @naveg