Add subs method for function field elements

[vincentmacri]

Fixes #38514.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

None

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[vincentmacri]

I'm not really sure what the rules/conventions are around using # needs sage.[whatever] in doc tests. I didn't use it in any of my tests because I wasn't really sure how/why it's used. Any feedback/guidance on that would be appreciated.

[vincentmacri]

@DaveWitteMorris could I get a review? (Asking since you triaged the bug report.)

[tscrim]

Here are my suggestions; please let me know if you have any questions.

[vincentmacri]

Thanks @tscrim! My only question is this one above:

I'm not really sure what the rules/conventions are around using # needs sage.[whatever] in doc tests. I didn't use it in any of my tests because I wasn't really sure how/why it's used. Any feedback/guidance on that would be appreciated.

[tscrim]

Thanks @tscrim! My only question is this one above:

I'm not really sure what the rules/conventions are around using # needs sage.[whatever] in doc tests. I didn't use it in any of my tests because I wasn't really sure how/why it's used. Any feedback/guidance on that would be appreciated.

Sorry, I forgot to answer that. Don’t worry about it; you do not need to add anything. It is for modularization that will be fixed by whomever knowns if something is necessary.

[vincentmacri]

Great! In that case is this ready to merge? I think the CI failures are unrelated. The tests pass on my machine at least.

[tscrim]

Indeed, I think this can be merged.