Update to v0.7.0

MANTIS 0.7.0 introduces multi-element isotope tracking with automated element grouping (derive_isotope_species_maps), allowing concurrent tracking of multi-isotope systems (e.g., $^{13}\text{C}$ and $^{34}\text{S}$) within combined reaction cascades. This release replaces iterative fixed-point speciation with a vectorized 1D Newton-Raphson solver in $\ln([\text{H}^+])$ for robust and rapid carbonate speciation convergence, adds explicit zero-, first-, and second-order reaction kinetic support, and expands declarative plotting with composite species evaluation (e.g. $\text{CaCO}_3$ and $\text{POC}$) and custom styling for measured benchmark data (measured_data_as). Furthermore, MANTIS 0.7.0 adds the Luff & Wallmann (2003) carbonate dissolution benchmark, coupled C–S isotope models, and updates core dependencies with scipy >= 1.18.1 and official Python 3.15 CI support.