[FEATURE REQUEST] ImageOutput.supports("quality")

**Is your feature request related to a problem? Please describe.**
There is no way to check if an output format supports a quality setting, other than scrubbing the code for uses of `decode_compression_metadata()`.
This is an issue for programs that want to expose quality in the GUI, especially when new formats are being added to OIIO.

**Describe the solution you'd like**
Add a "quality" feature for output formats
Of course that wouldn't always work with formats that support different compression methods (eg TIFF or EXR), but those are rather limited.

**Describe alternatives you've considered**
Testing for the format name manually and using prior knowledge about the format or scrubbing the OIIO source code.

Start by reading the ImageOutput interface and searching for uses of decode_compression_metadata(), which the issue identifies as the current way to infer support. Trace how output formats expose capabilities, then define and verify a quality feature that correctly reports support, including the noted TIFF and EXR compression cases.

Written by the indexing model from the issue text.