Fix tutorial_pulse_programming101.py to type cast expval

[andrijapau]

Context:

In PennyLaneAI/pennylane#6939, a fix was made to qml.expval so that it no longer silently converts the result to a real number. However, in tutorial_pulse_programming101.py we use a Hamiltonian with complex-typed coefficients. This resulted in an imaginary expectation value (X+0j) and broke the jax.value_and_grad function.

Description of change:

Wrap the qnode function to get the expectation value and convert it to a real number. This allows jax.value_and_grad to be used and fixes the demo.

[github-actions]

👋 Hey, looks like you've updated some demos!

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[github-actions]

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Deployment Info:

• Pull Request ID: 1317
• Deployment SHA: ef9343fb385774ac5d41e50606ce7f4924903f0f
  (The Deployment SHA refers to the latest commit hash the docs were built from)

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[PietropaoloFrisoni]

Thanks a lot @andrijapau!

[JerryChen97]

lgtm