python builder based on guppy's

[aborgna-q]

Expose guppy's hugr builder as a way to construct circuits using pure python.

This requires a user-friendly interface, either on the guppy or as a wrapper here.
Ideally the wrapper should only be a thin layer, to avoid code duplication.

[aborgna-q]

Blocked by CQCL/tket2#308

[ss2165]

Note this requires the new python hugr object to serialise and deserialise from the pydantic model