merge_rotations arbitrary angle ppr support

[kipawaa]

Context:
We've added arbitrary angle PPRs, but merge_rotations ignores them.

Description of the Change:
Adds support for arbitrary angle qec.ppr.arbitrary pprs to the merge_rotations pass.
The added rule merges PPRs as follows:

PPR(theta) * PPR(theta') -> PPR(theta + theta')

The rule supports conditions, re-ordering of Pauli words and qubits, and arbitrary sized PPRs.

Benefits:
merge_rotations simplifies QEC workflows as expected.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.06%. Comparing base (10b38c6) to head (3f869d3).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2258       +/-   ##
===========================================
- Coverage   97.57%   73.06%   -24.52%     
===========================================
  Files          93      143       +50     
  Lines       11245    14971     +3726     
  Branches     1076     1576      +500     
===========================================
- Hits        10972    10938       -34     
- Misses        208     3966     +3758     
- Partials       65       67        +2     

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[rniczh]

Thanks @kipawaa 💯 Just a fly-by comment

[paul0403]

Nice, just some final small things : )

[kipawaa]

@sengthai friendly reminder for review when you have the time :)

[paul0403]

Nice! @sengthai @lazypanda10117 either of you has time to give a second approval?

[lazypanda10117]

Nice! @sengthai @lazypanda10117 either of you has time to give a second approval?

I had a quick look and it looks good. It shouldn't conflict with my PR changes. Will do a proper review later today.