Control flow fallback

[albi3ro]

Context:

One of the challenges with turning autograph on by default is that it converts things it shouldn't convert into a structured for loop. When that happens, the whole program just fails and falls over.

To make things more user friendly, we instead just fall back to a standard python for loop. Less performant, but at least it works.

Description of the Change:

Fall back to standard python for loop if the capture of the jaxpr fails.

Benefits:

Things continue to run.

This fallback can be turned off by turning the qml.exceptions.CaptureWarning into an error.

Possible Drawbacks:

Things are unrolled, even if unrolled with a warning.

Related GitHub Issues:

[sc-103710]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.43%. Comparing base (dbdd8e4) to head (a5af99e).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8615      +/-   ##
==========================================
- Coverage   99.43%   99.43%   -0.01%     
==========================================
  Files         587      587              
  Lines       61885    61896      +11     
==========================================
+ Hits        61536    61546      +10     
- Misses        349      350       +1     

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