Remove Engine from InstanceConfig

[jprendes]

This PR removes the Engine generic from InstanceConfig.
As we move away from reusing one engine for all containers, we don't need to pass the engine around anymore.

This is a breaking change.

[jprendes]

Converting to draft until I figure out how to deal with the regression in wasmtime.

[jsturtevant]

As we move away from reusing one engine for all containers, we don't need to pass the engine around anymore.

This seems like the right thing to do since resolves a bunch of outstanding issues. This sharing of the engine was one of the "benefits" as I understood. It is such a small amount of shared memory/additional cpu, I don't think it will really be something that will be noticed but did we measure the chain against the bench mark at all?

[jprendes]

There seem to be a regression where wasmtime e2e tests are timing out, so that's a first indication.
But I think it's related to the pool allocator, which is allocating loads of virtual memory.
Before we were doing that operation once in the process, while now we do it twice per container.

@jsturtevant if you know how to get the benchmark reports for PRs, please let me know :-)