Function calculate_lebail_pattern_with_background 

pub fn calculate_lebail_pattern_with_background(
    pattern: &PatternRecord,
    instrument: ConstantWavelengthInstrument,
    phases: &[LeBailPhase],
    background: Option<&BackgroundModel>,
    support_fwhm: f64,
    execution: &ExecutionPolicy,
) -> Result<LeBailCalculation, LeBailError>

Calculate all fixed phases plus an optional analytical residual background.

The analytical values are added to, never substituted for, the fixed background stored by PatternRecord.

Errors

Returns LeBailError for invalid pattern, profile, or background state.