Deprecate pipeline=None with qml.compile

[albi3ro]

Context:

Currently, qml.compile has a default of pipeline=None, where None implies (commute_controlled, cancel_inverses, merge_rotations, remove_barrier). This is confusing, as None usually means "nothing".

Description of the Change:

Sets the default value to (commute_controlled, cancel_inverses, merge_rotations, remove_barrier) and deprecates passing pipeline=None.

Benefits:

Easier to determine default value from the call siganture.

Possible Drawbacks:

Just to make sure this looks good in the docs.

Is a deprecation.

Related GitHub Issues:

[sc-85186]

[andrijapau]

Thanks! This makes a lot more sense now. 😅

[Alex-Preciado]

Looks good!! Thank you so much @albi3ro 🚀

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.59%. Comparing base (4a5d44f) to head (98e86c5).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7004   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files         483      483           
  Lines       46066    46119   +53     
=======================================
+ Hits        45881    45934   +53     
  Misses        185      185           

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