fix: measure target qubits are required

[ashlhans]

Issue #, if available:

Description of changes:

The Circuit measure method target_qubits are not required.

Changes

• measure target_qubits are now required and there is no measure_all() equivalent
• Removed the error if the circuit is empty
• FreeParameter and float target qubits are not allowed. This will result in an error message
• Noise instructions cannot be added after a measure instruction
• apply_readout_noise gets added right after the last measure instruction instead of the very end of the circuit.

Testing done: tox and tox -e integ-tests

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (04d8a95) to head (7930cb1).

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[ashlhans]

Why remove measure_all functionality? If it's already released, wouldn't that be a breaking change?

@speller26, this shouldn't remove the qiskit measure_all functionality since that function measures each qubit individually behind the scenes (ie. for a 2 qubit circuit measure_all() is actually measure(0, 0) and measure(1, 1))

This would remove the already released measure() in the BDK but there are no examples that would break. There was some confusion with measure() without parameter, specifically whether that would measure all qubits or only currently used qubits. To prevent that confusion, we can make the target_qubit args required.