Avoid creating a temporary fork clone when nothing has changed from the template

[SamWilsn]

As an optimization to ForkCache.get, we should avoid creating a cloned fork if the clone would be identical to the template.

Originally posted by @SamWilsn in #1789 (comment)

[github-actions]

This issue has had no recent activity and has been marked as stale.

[JackCC703]

Hey, I’d like to take a stab at this.

From what I can tell, ForkCache.get should skip Hardfork.clone(...) when the requested overrides already match the template and just return the template directly.

Is that still the right direction on forks/amsterdam?