Add compatibility with psr/cache 3.0

[akalongman]

I am not able to install this package, because this requires a downgrading of my psr/cache from 3.0 to 1.0

[bshaffer]

This update will require a BC-break, so we should target it for v2.0 (see #322)

@akalongman What are you using google/auth for? As a stand-alone library, or as part of another library?

[bshaffer]

After looking into this, compatibility with psr/cache:3.0 will be difficult because it requires incompatibility with psr/cache:1.0. This means we'd essentially have to require PHP 8.0 to support it.

Another option would be to have two of every psr/cache-implementing classes. I am not a huge fan of this approach, but I don't see another way.

[akalongman]

@bshaffer I use this package with google apiclient.

[bshaffer]

@akalongman we've added support for psr/cache:2.0 in #344. As long as the library you're using also allows 2.0 then this will work without an issue once we tag our next release.

[bshaffer]

fixed in #348