Qubit allocation / discard.

[aborgna-q]

I'm trying to modify the planqc examples to work with the current runner.

This is the original rx example (plus some imports and module definitions).

from guppy.decorator import guppy
from guppy.module import GuppyModule
import guppy.prelude.quantum as quantum
from guppy.prelude.quantum import Qubit, h, measure, rz

module = GuppyModule("module")
module.load(quantum)

@guppy(module)
def rx(q: Qubit, a: float) -> Qubit:
  # Implement Rx via Rz rotation
  return h(rz(h(q), a))

@guppy(module)
def main() -> bool:
  q = Qubit()
  r = rx(q,1.5)
  return measure(r)

This tries to allocate a qubit calling Qubit(), and assumes that measure is destructive.
We do not currently have a qubit allocation method, and measure is Qubit -> (bool, Qubit).

If we want to keep this structure, we need a pair of quantum alloc/free functions.

[ss2165]

Also blocked by: CQCL/tket2#283