Custom formatting of std::string

I have some tests that use `std::string`s with various non-ascii chars.

If one of the tests fail, it would be very convenient to output the string contents in eg. hex format instead of letting catch print the output as a normal `std::string`.

For good reasons it is not possible to specialize the `<<` operator for strings and it doesn't seem to be possible to override the default `StringMaker` implementation - at least not for a specific test case/executable.

Of course there are ways around this, but all I can think of is not very elegant and I really like the simplicity and elegance of catch2 so I'm wondering if there's some way of handling that case?

If not, I was wondering if it was something that could be implemented somehow? I could imagine there could be other cases where a user would like to have a "standard type" formatted differently?

Thanks a lot and thanks a lot for this great framework!

Start by reading Catch2's StringMaker implementation and the existing customization behavior for std::string. Investigate how formatting can be scoped to a specific test or executable, then define a focused API and tests covering non-ASCII strings and hexadecimal output.

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