GDA: Axis constraint Scannables naming convention is unintuitive ('You' engine)

Where an axis (e.g. gamma) may be fixed by a constraint an _con Scannable is created rather than an Scannable in order to avoid a namespace clash with that axis' actual Scannable. This is unintuitive.

One solution is for Diffcalc to read up the last set value for an axis when that axes is constrained.

However if the axis is Scanned while hkl is held still this would result in two motor moves. This could be resolved by making the physical axis Scannables the same level as the hkl Scannable and treating them as a group, although this is a pretty heavy solution.

首先跟踪 GDA 如何创建轴约束 Scannables，以及物理轴扫描和 hkl 扫描是如何处理的。将提议的最后值查找与分组 Scannable 方法进行比较，尤其注意避免两次电机移动。当扫描某个轴而 hkl 保持不动时，命名约定仍然直观且不会导致重复移动，即视为完成。

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