Cleanup

[szabo137]

During the restructuring of QED.jl, some little cosmetic issues were introduced (or copied):

• [ ] check for obsolete dependencies (in deps and extras)
• [ ] Drop usage of Suppressors in the tests and use TestImpl instead.
• [ ] rename algebraic_objects
• [ ] use import Pack and Pack.func(...) = ... instead of using Pack: func and func(...) = ... for implementing an interface.
• [ ] move all import statements to src/QEDcore.jl
• [ ] Drop usage of SimpleTraits.jl (maybe after https://github.com/QEDjl-project/QEDbase.jl/issues/59)
• [ ] refactor src/particles/spinors.jl (will be done in a separate issue)
• [ ] reexport base_state (?)
• [ ] remove mul because it is redundant if Base.* is implemented anyway.