CI improvement: unify json rpc caches

[anaPerezGhiglia]

• we could use cross OS caché for JSON rpc cache - we store .json files that are not specific to the platform https://github.com/actions/cache/blob/main/tips-and-workarounds.md#cross-os-cache
• we could save RPC caché only in main branch workflows and in the rest just restore it
• Or we could force the deletion of closed-PR caches to prevent caches from default branch getting thrashed. https://github.com/actions/cache/blob/main/tips-and-workarounds.md#force-deletion-of-caches-overriding-default-cache-eviction-policy

More context in: https://github.com/NomicFoundation/edr/blob/chore/ci-workflow-caches/notes/workflow-caches.md

[Wodann]

We can set a common JSON-RPC directory at the workspace root for all of our JSON-RPC provider tests in the ProviderConfig. This will allow reuse of caches between integration and units tests.