Pow Symbolic Operator

[albi3ro]

This class mirrors the symbolic operators being introduced in #2222 and #2475 .

This PR will only introduce the symbolic operator and not add a user-facing constructor or device execution support.

[github-actions]

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[codecov]

Codecov Report

Merging #2621 (09d0324) into master (43fc4f6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           master    #2621    +/-   ##
========================================
  Coverage   99.58%   99.58%            
========================================
  Files         248      249     +1     
  Lines       19985    20135   +150     
========================================
+ Hits        19902    20052   +150     
  Misses         83       83            

Impacted Files	Coverage Δ
pennylane/math/single_dispatch.py	98.86% <ø> (ø)
pennylane/ops/op_math/__init__.py	100.00% <100.00%> (ø)
pennylane/ops/op_math/pow_class.py	100.00% <100.00%> (ø)

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[albi3ro]

[sc-20183]

[antalszava]

Got a glimpse of the overall operator arithmetic, an amazing push @albi3ro! 🎆 It's apparent that much thought went into the planning and the design here.

Left some comments, many for my own understanding.

[mariaschuld]

Nice!

I admit I had a superficial review to check the general logic and test coverage, so my "accept" would be subject to at least one more acceptance. But since this recovers the structure of the previous PR I would trust that it works as there.

[antalszava]

Looks good! 🎉 🙂 Amazing to see that a consistent and clear structure is being created here. 🏛️