Guppy's measure_array is too eager

[jake-arkinstall]

In guppy, measure_array returns array(measure(q) for q in qubits)

It should be expected that this, after some optimisation, can be expressed as two loops - the first requesting futures, the second reading them. Guppy doesn't have a concept (that I'm aware of) of measurements as futures, so this would probably need to happen in an optimisation pass (hence this being a tket2 issue).

We do have some optimisation that streamlines measurements of multiple qubits into more optimal lazy measurements within a function, e.g. see #432, but this is not taking effect for measure_array. Instead, each qubit is measured individually, making the measurement of qubit arrays less efficient than it should be.