Move tket2's `CircuitHash` here

[aborgna-q]

CircuitHash is already implemented for HugrViews with a dataflow-container root. It should be easy to expand it to arbitrary hugrs (and rename it to HugrHash).

https://github.com/CQCL/tket2/blob/main/tket/src/circuit/hash.rs

[aborgna-q]

As a drive-by, it should be easy to add support for TailLoops and Conditionals, and add better docs saying that CFG childrens are not supported.