Null qubit supports any operation without a decomposition

[albi3ro]

Context:

Description of the Change:

null.qubit will now automatically support any operation that doesn't have a decomposition.

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[sc-61258] Fixes #5508

[github-actions]

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[DSGuala]

Tested this with qml.QuantumPhaseEstimation, qml.TrotterProduct, the code from issue #5508, the qml.resource documentation example, and the error estimation demo draft.

Looks like it's working as intended. Defining a decomposition for an ErrorOperation destroys the error information in qml.Tracker. But that's according to plan. We can decide how to address this in the next release and users who want to define decompositions for error ops can use default.qubit in the meantime.

👍 👍

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.69%. Comparing base (9151477) to head (af75b2c).
Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5582      +/-   ##
==========================================
- Coverage   99.69%   99.69%   -0.01%     
==========================================
  Files         410      412       +2     
  Lines       38278    38237      -41     
==========================================
- Hits        38161    38119      -42     
- Misses        117      118       +1     

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