Unify error message for better Catalyst support

[multiphaseCFD]

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---

Context:

Unify error messages of shot measurement related unsupported observables to better Catalyst.

Description of the Change:

For the moment, shot measurements support Paulis, Identity and Hadamard obs and TensorProd/Hamiltonian obs created based on above mentioned named obs. Error messages are thrown inside each shot measurement method. Now error messages are obs based and it will support Catalyst better.

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (998362a) 98.95% compared to head (d9d304d) 98.68%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #577      +/-   ##
==========================================
- Coverage   98.95%   98.68%   -0.28%     
==========================================
  Files         167      167              
  Lines       24382    23959     -423     
==========================================
- Hits        24128    23644     -484     
- Misses        254      315      +61     

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[AmintorDusko]

@multiphaseCFD, could you please fill-out the PR description?

[multiphaseCFD]

@multiphaseCFD, could you please fill-out the PR description?

Thanks @AmintorDusko . Done!

[vincentmr]

Looks good to me, cheers @multiphaseCFD !

[AmintorDusko]

Nice work @multiphaseCFD! Thank you for that!

[maliasadi]

Hey Shuli, Would you like to include the patch to address the following issue as well?

var(TensorProd, num_shots=5000) using the C++ API in both Lightning and LightningKokkos returns zero for the following circuit:

@qml.qnode(dev)
def circuit():
    qml.PauliX(0)
    qml.PauliY(1)
    qml.Hadamard(2)
    qml.PauliZ(3)
    return qml.var(qml.PauliX(2) @ qml.PauliY(1) @ qml.PauliZ(0))

>>> circuit()
0.99983616

[multiphaseCFD]

[565387d](/PennyLaneAI/pennylane-lightning/pull/577/commits/565387d46aa08c47e5b2d843a9e888f3e56ba266)

Hey @maliasadi , just tested the circuit you mentioned above with 565387d and tests passed in C++ backend.