ArjunChakrawal/chemodiv-litter-model: v2

Source-separated litter decomposition model with microbial necromass recycling This release adds a source-separated litter decomposition model that tracks plant-derived organic matter and microbial necromass separately for each NMR-derived compound class. Lignin protection is applied only to plant-derived carbohydrate and N-bearing pools, preventing microbial residues from being treated as lignin-protected plant material. Key updates: Added plant and necromass pools for all five compound classes. Added microbial turnover inputs into chemically defined necromass pools. Updated N balance for source-separated protein/N-bearing pools. Weighted oxidative enzyme costs by the plant-derived fraction of total uptake. Retained the same five fitted decomposition rate constants. Added diagnostics for necromass contribution, effective protection, enzyme-cost dynamics, and comparison with the lumped model. This release improves interpretation of N-bearing compound accumulation and microbial residue turnover while preserving direct comparison with observed total compound pools.