[CI] Layout CI does not work from forked repos

[MaxMustermann2]

The proposed solution is to split the CI into 2.

• The first works on the PR + base branch and is triggered by pull_request. It caches the layouts from the PR (and the base branch for ExocoreGateway)
• The second works after the first one has been triggered using workflow_run and compares the cached layouts + calls to cast storage.
• Instead of using our custom Python script, we should use the tooling provided by OpenZeppelin to compare these layouts.

I have implemented most of this but it needs to be tested. PR foundry-rs/foundry#9332 adds support for cast storage to export the JSON layouts. Now that it has been merged, I will wait for a nightly release that includes this change and test it out on my fork before sending the PR out.