Extend complexity bounds for TNIFs

Background: The complexity of simulating non-Markovian open quantum systems is often determined by the number of exponential terms required to approximate bath correlation functions (BCFs).

Question / Future Work: The paper establishes rigorous complexity bounds for approximating BCFs using sums of exponentials for systems coupled to Gaussian baths with general spectral densities. Future work may involve extending these complexity analysis techniques to tensor network influence functionals beyond the Ohmic case, specifically to super-Ohmic and sub-Ohmic spectral densities.