Function run_tgv 

pub fn run_tgv(
    phases: &[&[f64]],
    magnitudes: Option<&[&[f64]]>,
    mask: &[u8],
    metadata: &ScanMetadata,
    field_mapping_config: &FieldMappingConfig,
    tgv_params: &TgvParams,
    reference: QsmReference,
    progress: &mut dyn FnMut(usize, usize),
) -> Result<Vec<f64>, PipelineError>

Run TGV single-step QSM reconstruction.

For multi-echo data, runs field mapping first to get B0, then converts to phase at TE1. For single-echo, uses wrapped phase directly. TGV internally handles unwrapping + background removal + inversion.

Returns

Susceptibility map in ppm (unreferenced — call apply_reference after)