[FEATURE REQUEST] Hue/Saturation adjustments in ImageBufAlgo

It would be very handy to have function(s) in ImageBufAlgo to adjust hue/saturation of the image.
Either all image or some masked region.

Having a case where region filled with `fillholes_pushpull()` calls needs saturation adjustments.
Currently have to do it externally. Would be very handy to do inside of OIIO.

It could be nice to match those operations to similar operations from popular Nuke software from The Foundry.
Please take it as suggestion only.

For saturation it would be `Saturation` node from Nuke with two parameters.
Float "Saturation" and enum "luminance math" which is usually set to rec709.
For hue it would be `HueShift` node.

Can also use any other math that helps dialling saturation and changing hue.

Thank you.

Start by reviewing the ImageBufAlgo API and the existing fillholes_pushpull() operation mentioned in the issue. Compare the requested hue and saturation behavior with Nuke's HueShift and Saturation nodes, including masked-region handling and rec709 luminance math. Done means agreed function signatures, defined adjustment behavior, and corresponding tests.

Written by the indexing model from the issue text.