Remove usage of qml.Hamiltonian from hamiltonian.py

[astralcai]

hamiltonian.py defines the legacy Hamiltonian. It should not be returning LinearCombination in its own methods even with new op math enabled.

[github-actions]

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[astralcai]

[sc-59501]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.48%. Comparing base (5013e4b) to head (a18552f).
Report is 12 commits behind head on ham-tests.

Additional details and impacted files

@@            Coverage Diff             @@
##           ham-tests    #5429   +/-   ##
==========================================
  Coverage      99.48%   99.48%           
==========================================
  Files            400      400           
  Lines          37146    37146           
==========================================
  Hits           36954    36954           
  Misses           192      192           

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[lillian542]

🎉

[Qottmann]

same for this, wait for ham-tests CI to pass before merging