switch SOuterProduct from `*` to `projector`

[Krastanov]

PR #104 was necessary because of the choice below:

QuantumSymbolics.jl/src/QSymbolicsBase/basic_ops_inhomogeneous.jl

Line 122 in de5fba9

operation(x::SOuterKetBra) = *

Maybe we should revert that PR and instead change SOuterProduct to use projector

Or upstream the * -> projector conversion to QuantumOpticsBase and still revert #104.