NumOrString trait not implemented for f32

[crystal-growth]

NumOfString trait implementation is missing for f32 type, preventing from using it in defining axis ranges:

let (xmin:f32, xmax:f32) = some_func();
...
let layout = plotly::Layout::new()
 .x_axis(Axis::new().range(vec![xmin, xmax]).auto_range(false))

results in compilation error:

the trait `ptly::plotly::private::NumOrString` is not implemented for `f32`

requiring manually casting f32 to f64:

...
.x_axis(Axis::new().range(vec![xmin as f64, xmax as f64]).auto_range(false))
...

that looks less ergonomic.