feat: Add optional min/max statistics to info file for numeric data

In imagery, precomputed annotations, and precomputed skeletons, numeric properties typically have a natural range set by the data, independent of the dtype used (particularly for annotation floats). Neuroglancer currently handles those best using inverlp, which can infer percentile statistics from loaded data. In many cases, whoever is building the info file has or can have a good handle on the intended range of the data at the time of writing the info file.

A quality-of-life feature for generating better default visualizations would be an optional min/max parameter within the annotation property in the info (or equivalent location in other layer types) for numeric data types without an `enum_values`/`enum_labels` configuration. This could then be used to build the shader elements with data-relevant values without having to actually load any data. Because the actual shader is determined by the user, these values just set a sensible default and could be overridden at any time by adjusting the shader or shader ui controls.