[Decomposition] Clean up custom logic for adjoint and pow

[astralcai]

Context:

This is a follow-up PR to #7347

Description of the Change:

There was previously a lot of custom logic for retrieving decomposition rules of symbolic operators. With the infrastructure added in #7347, this PR is able to clean up most of it.

• We no longer hard-code a list of operators whose adjoint is an instance of the same type. Instead, each operator with a custom adjoint decomposition registers a decomposition rule for the adjoint of itself. For example, Hadamard was previously hardcoded as an operator that is its own adjoint, now there is a decomposition rule for "Adjoint(Hadamard)" which produces an instance of the base operator.
• We removed the constraint that powers of an operator must be integers. Non-integer powers can be supported by adding custom decomposition rules for "Pow(SomeOp)". All operators in PL which overrides pow now has a custom decomposition rule registered under the power of itself.
• Defined some general stock decomposition rules that can be registered under any operator. For example, a self_adjoint decomposition rule is defined, and it is registered with all operators that are self-adjoint (to avoid having duplicate code)

Related Shortcut Stories:

[sc-90114]

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.69%. Comparing base (0346190) to head (66b2bfb).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #7352    +/-   ##
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  Coverage   99.69%   99.69%            
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  Files         537      537            
  Lines       50954    51197   +243     
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+ Hits        50799    51042   +243     
  Misses        155      155            

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