Support parameter broadcasting with GlobalPhase

[dwierichs]

Context:
GlobalPhase does not support broadcasting yet.

Description of the Change:
Introduce broadcasting to GlobalPhase, using the code from PauliRot with set(pauli_word) == {"I"}.
The latter falls back to the GlobalPhase implementation.

Also fixes a small bug where the global phase returned by one_qubit_decomposition gains a broadcasting dimension even if the input matrix does not have one.

Benefits:
Broadcasting support & Bug fix

Possible Drawbacks:

Related GitHub Issues:
Implements #5815

[sc-65316]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.66%. Comparing base (e74c9bf) to head (29cc5c5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5923      +/-   ##
==========================================
- Coverage   99.67%   99.66%   -0.01%     
==========================================
  Files         425      425              
  Lines       40772    40479     -293     
==========================================
- Hits        40640    40345     -295     
- Misses        132      134       +2     

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