Scan CalcType + ScanData + Tests

[TroyNSmith]

• Added Scan to the CalcType enum class
• ScanData holds a trajectory of ProgramOutput[ProgramInput, OptimizationData]
• ScanData.energies gives all of the optimization final energies
• ScanData.structures gives all of the optimization final structures
• Added test_scan_data.py with tests mirroring test_optimization_data.py

[avcopan]

@coltonbh This PR is ready for review. We want to hold off on generalizing for frozen scans for now, because we don't have a good way of testing it yet.

[coltonbh]

Made a few small fixes and then merged:

• Moved ScanData.model_rebuild() to outputs.py, consistent with other *Data objects that rely on ProgramOutput.
• Removed ProgramOutput and ScanData.model_rebuild() from test file.
• Added ScanData to StructuredData union object.

[avcopan]

Thanks, @coltonbh!

[coltonbh]

@avcopan and @TroyNSmith if/when you need versioned releases of this let me know. I can release versions along the way if it makes a meaningful difference for you, or wait until the work is more complete (e.g., the frozen scan piece).

[avcopan]

@coltonbh It would be helpful to go ahead and do the versioned release!

[coltonbh]

Released as 0.17.1. Welcome onboard as a contributor, @TroyNSmith! 🎉