Reinstate Lanczos as the default solver for hermitian systems

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files	Coverage Δ
src/algorithms/ED.jl	`100.00% <ø> (ø)`
...c/algorithms/excitation/quasiparticleexcitation.jl	`81.45% <100.00%> (+0.49%)`	:arrow_up:
src/algorithms/groundstate/dmrg.jl	`100.00% <100.00%> (ø)`
src/algorithms/groundstate/idmrg.jl	`100.00% <100.00%> (ø)`
src/algorithms/timestep/tdvp.jl	`93.05% <100.00%> (ø)`
src/utility/defaults.jl	`52.17% <100.00%> (+4.55%)`	:arrow_up: