Algorithm for finding qubit operations subgraphs

[ss2165]

Using: CQCL/hugr#1541

Given a hugr lazily return an iterator over subgraph boundaries, where the subgraphs are made up of qubit operations.
Operations:

• unitaries (incl parametrised by angle, but not including ops on just angles)
• alloc/reset
• measure/free

These subgraphs can then be extracted and converted to pytket

[aborgna-q]

Once we find the subgraphs it may be useful to reuse/generalize the CircuitChunks definition, as it has the logic for gluing the chunks back.

Alternatively, @doug-q suggested doing a pass that moves each subgraph to a DFG region, which can be extracted/replaced as a whole region.