v0.5.3

Add broader symbolic math coverage — syms, sym, symbolic function declarations such as syms y(x), symbolic powers, and scalar limit workflows now execute through parser, HIR, runtime, VM, and WASM paths. Add signal, linear-algebra, and math builtins — hilbert, unwrap, pulstran, rectpuls, tripuls, gauspuls, upsample, downsample, null, and heaviside now cover common signal-processing, numeric, and symbolic scripts. Add spreadsheet and file-selection workflows — spreadsheetImportOptions, uigetfile, expanded path commands, and provider-aware cd behavior now work across local, sandboxed, remote, and WASM filesystem providers. Add root-locus plotting and output forms for transfer-function models. Expand MATLAB command and call syntax support, including command-form path arguments, grid minor, axis image, and name-value call arguments written as Name=value