Fix #17354: Preserve class binding in classmethod flows when using

[vilhenad]

Classmethod flows were losing their cls inheritance structure when copied with .with_options(), causing them to default to the base class implementation. This was particularly evident when subclassing (e.g., ChildProcessor.process would incorrectly use BaseProcessor.get_multiplier).

The fix ensures proper context preservation by:

1. Creating deep copies of the function for each bound flow
2. Maintaining independent prefect_self references
3. Preserving all function attributes during copying

Added test cases verify:

• Classmethod inheritance is maintained after .with_options()
• Instance methods retain their proper self context
• Multiple bound flows don't interfere with each other

Closes #17354

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

[codspeed-hq]

CodSpeed Performance Report

Merging #17647 will not alter performance

_{Comparing vilhenad:fix-classmethod-flow-bug-17354 (518f246) with main (de45c87)}

Summary

✅ 2 untouched benchmarks

[desertaxle]

Thanks for the PR @vilhenad! I think it makes more sense to move the copying logic into .with_options, since copying the function shouldn't be necessary during normal execution. Copying it on every call could increase memory usage for instance method flows.

[vilhenad]

Thank you for the quick review @desertaxle! I completely understand your point on increasing memory usage. However, if you don't mind clarifying, I've got a question. As you can see by my second unit test, this fix also addresses instance methods not preserving context when using a flow (without .with_options). Should I just carry through with only making changes to the .with_options (consequently discarding this other fix)?

[desertaxle]

@vilhenad I made some changes in #17660 that address the issue covered by your second unit test, so I think you should focus on only the issue with .with_options in this PR.

[vilhenad]

@desertaxle I've pushed the changes you requested. One thing is confusing me: my unit test is passing fine locally, but consistently failing in the GitHub CI. The test code appears identical to the example from the issue page and works in isolation locally.
Wondering if you have any insights into why the CI environment might be behaving differently?

[desertaxle]

Thanks for making those updates @vilhenad!

I think it's failing on 3.13 because of changes in 3.13 that made @classmethod no longer chainable. I added the _isclassmethod and _isstaticmethod attributes in #17660 to handle that change, and I think that they'll need to be copied over in .with_options for the functionality in this PR to work with 3.13.