make CompositeOp.eigendecomposition jit-compatible

[timmysilv]

Context:
Similar to #5206 - state_diagonalizing_gates depends on the eigendecomposition which is not jit-compatible.

Description of the Change:
use qml.math throughout eigval computation in order for it to be jit-compatible

Benefits:
Anything depending on the eigendecomposition (eg. measuring an observable with abstract data) will now work with jit

Possible Drawbacks:
The solution in #5206 might be more performant? I have closed that PR, but pls lmk if you think I should re-open it.

[sc-56801]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (256b1cc) 99.68% compared to head (d95dff8) 99.68%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5207      +/-   ##
==========================================
- Coverage   99.68%   99.68%   -0.01%     
==========================================
  Files         396      396              
  Lines       36640    36366     -274     
==========================================
- Hits        36526    36251     -275     
- Misses        114      115       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Qottmann]

Thanks @timmysilv

Could still be worth looking into the other solution and using dot products whenever there is a matrix representation of the observable available