feat(oiiotool): enhance expressions with string formatting operator

[lgritz]

It would be handy for the command line expression syntax (things like {2 * TOP.width}) had a fully general way to do string formatting.

This may be kind of involved, but I think it's worth doing.

We'll use this issue to track progress and flesh out a spec for it.

As a motivating example, see #5207, where we posit the utility of something like

--offset "{format('{:+}{:+}',X,Y}"

There's a bit of ugliness coming from the fact that we use {} in oiiotool for indicating expressions, but also {} inside the format specifications, and I'm not sure if it will end up needing special quoting. But the advantage of going for a fully general formatting utility that can be used in expression evaluation means that it not only solves your problem, but likely also unlocks a whole bunch of interesting additional usages.

[MrLixm]

Hey,
Totally agree !
It would be very nice to have, without being essential, but it does indeed looks like complex to implement.
Just throwing this here, there could be some inspiration taken from python fstring syntax: https://docs.python.org/3.14/reference/lexical_analysis.html#formal-grammar-for-f-strings.