Add numpy-style ToString method

[dayo05]

New method is exists on Tensor::str(). I'll create more tests for that.

[NiklasGustafsson]

This belongs in TensorExtensionMethods, I think.

[NiklasGustafsson]

Another possibility is to add a 'style' argument to the verbose ToString() that currently takes a boolean.

Instead of

public string ToString(bool withData, string fltFormat = "g5", int width = 100, CultureInfo? cultureInfo = null)

it would be something like this:

public enum TensorStringStyle { Metadata, Julia, Numpy }

public string ToString(TensorStringStyle style, string fltFormat = "g5", int width = 100, CultureInfo? cultureInfo = null) 
{
    if (style == TensorStringStyle.Metadata) return ToString();
    ...
}

// For backward compat:

public string ToString(bool withData, string fltFormat = "g5", int width = 100, CultureInfo? cultureInfo = null) 
{
    return ToString(withData ? TensorStringStyle.Julia : TensorStringStyle.Metadata, fltFormat, width, cultureInfo);
}

[dayo05]

Then how about this?

public static TensorStringStyle DefaultOutputStyle = TensorStringStyle.Metadata;

            public override string ToString() => ToString(DefaultOutputStyle);

            public string ToString(TensorStringStyle style, string fltFormat = "g5", int width = 100,
                CultureInfo? cultureInfo = null) => style switch {
                    TensorStringStyle.Metadata => ToMetadataString(),
                    TensorStringStyle.Julia => ToJuliaString(fltFormat, width, cultureInfo),
                    TensorStringStyle.Numpy => ToNumpyString(this, ndim),
                    _ => throw new InvalidEnumArgumentException("Not supported type")
                };

[NiklasGustafsson]

Sure. Don't you want CultureInfo and fltFormat on the NumPy string?

[NiklasGustafsson]

Maybe this should also take a style argument, but defaulted to 'Julia,' not 'Metadata' There could also be a 'npstr()' that defaults to NumPy. Same for print().

[NiklasGustafsson]

New test failures. This time, I think it's because of the tests doing this:

.Select(x => x * 2.5 + 5)

which leads to rounding differences in various runtimes.

For a test like this, I think you probably want to have a fixed collection of numbers, not involving any FP arithmetic, so that you avoid the risk of rounding or other arithmetic-related errors.

[NiklasGustafsson]

@dayo05 -- I just merged your changes. Looking good!

With this, I will prepare and make a new release later today.