Hybrid QNN and VQE samples do not work with an external QPU provider

[nkushida-oqc]

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Describe the bug

After applied this PR, I tried to run Hybrid QNN sample with OQC's QPU. However, I got the following error;
`TypeError: init(): incompatible constructor arguments. The following argument types are supported:
1. cudaq.mlir._mlir_libs._quakeDialects.cudaq_runtime.ObserveResult(arg0: float, arg1: cudaq::spin_op, arg2: cudaq.mlir._mlir_libs._quakeDialects.cudaq_runtime.SampleResult)

Invoked with: None, <cudaq.mlir._mlir_libs._quakeDialects.cudaq_runtime.SpinOperator object at 0x7ffb61af9270>, <cudaq.mlir._mlir_libs._quakeDialects.cudaq_runtime.SampleResult object at 0x7ffb5e346cf0>`

Another example is https://nvidia.github.io/cuda-quantum/0.8.0/examples/python/tutorials/vqe.html;
This gives;
python3: /home/.llvm-project/mlir/lib/IR/PatternMatch.cpp:276: virtual void mlir::RewriterBase::eraseOp(mlir::Operation*): Assertion op->use_empty() && "expected 'op' to have no uses"' failed.
Aborted (core dumped)
`

However, Max Cut example (https://nvidia.github.io/cuda-quantum/latest/applications/python/qaoa.html) seems to be working.
One of CPP test codes also works;
https://github.com/NVIDIA/cuda-quantum/blob/7b4222430542fe87b103ba58bf94dde5c875e739/targettests/execution/cudaq_observe.cpp

Steps to reproduce the bug

qnn.py.txt
QNN code is the above.

vqe.py.txt
VQE code is the above

Expected behavior

Reproduce the same result with the samples with local simulators.

Is this a regression? If it is, put the last known working version (or commit) here.

Not a regression

Environment

• 0.8.0:
• 3.10:
• GCC12/LLVM16:
• Ubuntu 22.04:

Suggestions

It seems to be that an internal transpiler/compiler could not generate QIR for some reasons.

[bmhowe23]

With all the latest fixes from main, this is no longer producing the errors provided in the original issue description, but it is failing in different ways. For example, the attached VQE example fails with:

error: 'cc.loop' op not a constant upper bound loop
...
error: 'cc.loop' op loop bounds exceed iteration threshold
...
error: did not unroll loops
RuntimeError: NLOpt runtime error: nlopt failure
...

(This can also be reproduced by running with the emulate flag, like this: cudaq.set_target("oqc", emulate=True).)

This particular example uses cudaq.kernels.uccsd(), which may exceed the limits to which the loops can be unrolled.