docs: Conversion of ImageOutput docs to tests for the copy image exam…

[demiaster]

Description

Convert C++ and Python example from the ImageOutput: Copying an entire image chapter into tests within the docs-examples-{cpp,python} test suites.
This was done following the steps outlined in Converting documentation examples to tests.

---

• This PR contributes to addressing issue Convert documentation examples into testsuite tests #3992.
• This PR supersedes the closed PR test: add docs example imageoutput copy #5195.

---

Notes

• In both python and cpp I have replaced the file {input,output}.jpg mentioned in the example with {input,output}.exr in the test, so to reuse existing resource files (i.e. testsuite/common/grid-small.exr): do let me know if you prefer the tests also use a .jpg, in which case I'll add a new resource to that effect.
• The cpp example code was further modified to:
  1. pass the requirements of clang-format (see original failing output here)
  2. successfully run ImageOutput.copy_image
• The python example code was further modified to remove unnecessary whitespace before the brackets of function calls.

Finally, when following the conversion docs, I have not addressed point 5: again, let me know if you prefer to have a positive fixture to compare the test output against.

Tests

I have checked that, on my fork:

• The CI passes successfully: https://github.com/demiaster/OpenImageIO/actions/runs/25888576608
• The docs build successfully: https://github.com/demiaster/OpenImageIO/actions/runs/25888576599
• The replaced docs examples render correctly (see excerpt from above build here: imageoutput.html)

Checklist:

• I have read the guidelines on contributions and code review procedures.
• I have read the Policy on AI Coding Assistants
  and if I used AI coding assistants, I have an Assisted-by: TOOL / MODEL
  line in the pull request description above.
• I have updated the documentation if my PR adds features or changes
  behavior.
• I am sure that this PR's changes are tested in the testsuite.
• I have run and passed the testsuite in CI before submitting the
  PR, by pushing the changes to my fork and seeing that the automated CI
  passed there. (Exceptions: If most tests pass and you can't figure out why
  the remaining ones fail, it's ok to submit the PR and ask for help. Or if
  any failures seem entirely unrelated to your change; sometimes things break
  on the GitHub runners.)
• My code follows the prevailing code style of this project and I
  fixed any problems reported by the clang-format CI test.
• If I added or modified a public C++ API call, I have also amended the
  corresponding Python bindings. If altering ImageBufAlgo functions, I also
  exposed the new functionality as oiiotool options.

[lgritz]

This looks great! Thanks for the contribution.

The formality and structure of your PR description makes me think you used an AI coding assistant to help with this work. That's fine, but if true, we would prefer that you disclose that with a line in your PR description that looks like:

Assisted-by:  TOOL-NAME / MODEL-NAME

Just edit the PR description and let me know when you've done that so I can merge. Or, if this is really all your own brain's work, just say so.

[demiaster]

Hello @lgritz, thank you for reviewing!

The formality and structure of your PR description makes me think you used an AI coding assistant to help with this work.

No AI used for this PR: the way the work is presented was an attempt on my part to ensure anyone coming in had the best possible context to conduct a review asynchronously 😄

Let me know if you want me to say as much in the PR description also, or whether the comment here is enough.

[lgritz]

No, it's not a problem at all. I just wanted to ensure that any assisted-by attribute, if needed, was added before I did the merge (after which I can't change it).

All looks good, I will merge. Thanks for this patch!