Algorithm: `CalibrationMetricExtractionAlgorithm`
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Description:
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This algorithm extracts calibration metrics from the output of the peak
fitting algorithm `FitMultiplePeaks`. It calculates the sigma and strain
averages and standard deviations, and then packages them with the
two-theta average. This is done per group, with strain and sigma
collected over spectra within the group.

Expected Inputs:
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1. **InputWorkspace**:
   - **Type**: `WorkspaceGroup`
   - **Direction**: `Input`
   - **Property Mode**: `Mandatory`
   - **Description**: Group of workspaces containing the peak fitting results.

2. **PixelGroup**:
   - **Type**: `String`
   - **Direction**: `Input`
   - **Property Mode**: `Mandatory`
   - **Description**: JSON string defining the pixel group.

Expected Outputs:
-----------------
1. **OutputMetrics**:
   - **Type**: `String`
   - **Direction**: `Output`
   - **Property Mode**: `Optional`
   - **Description**: JSON string containing the extracted calibration metrics.