synth-nmr: NMR spectroscopy calculations for protein structures

A lightweight, standalone Python package for calculating NMR observables from protein structures. Provides tools for NOE distance restraints, R1/R2/heteronuclear NOE relaxation rates, chemical shift prediction (SHIFTX2 with SPARTA+ fallback), J-couplings via the Karplus equation, residual dipolar couplings (RDCs), ensemble/MD-averaged NMR observables, and NMR Exchange Format (NEF) I/O. Originally extracted from the synth-pdb package to provide a focused toolkit compatible with any protein structure source including PDB files, AlphaFold predictions, and MD simulations.