Some general FinBaseSim-related TODOs

[schuderer]

• [x] Specify variables in init of FinBaseSimulation: self.time = 0
• [x] Resoucre["cash"] type did not expect str
• [x] error when calling run before reset -- Did not add an error, but documented the "reset before run" requirement
• [x] self.world.np_random does not exist -- Note: did not yet implement seed() in the sim_env
• [x] repr of entities always prints "Entity(...)" -- also added repr to other classes in fin_base_sim
• [ ] import warning box bound precision lowerd by ... float32 -- could not reproduce yet
• [x] actually test all of above fixes ;)