dsh-chem: A Deterministic Chemical Computation Plugin for DeepSeek Harness

`dsh-chem` is a DeepSeek Harness plugin designed to address arithmetic errors in chemical calculations by large language models. It replaces LLM mental math with deterministic algorithms and provides six core functions based on IUPAC data: chemical formula parsing and molar mass calculation, mass/mole/particle conversions, solution concentration calculations, pH/pOH and buffer solution calculations, chemical equation balancing, and ideal gas law arithmetic. The plugin supports complex scenarios such as nested parentheses, hydrates, and ionic charges, and behaves honestly by explicitly reporting an error for equations that cannot be balanced. Before installation, ensure that the Node.js version is 20 or higher.