feat: add termination on root mismatch in store

[drahnr]

When the store finds itself in a situation where the nullifier tree update doesn't align with the nullifier root in the block_header

Review notes:

• uses an mpsc so we don't have to Option wrap, we can have multiple concurrent requests that trigger the code-path, having channel capacity small means the first to hit the path will block all following ones and trigger termination
• State::load is not called via RPC, so the error does terminate correctly

Closes #1328

[Mirko-von-Leipzig]

Only question for me is whether this is the correct sync primitive, but its probably just semantics tbh. e.g. https://docs.rs/tokio/latest/tokio/sync/struct.Notify.html.

[drahnr]

I considered notify, but then we'd lose context on what failed, and I am not aware of a better primitive to transfer a few bytes.