Update API docs for v2026.2

[matthew-white]

This PR is to track changes that we need to make to the API docs for v2026.2. If a PR makes a change to the API and simultaneously changes the API docs, then that change doesn't need to be listed here.

⚠️ If there is a breaking change to the API, an issue should be filed with pyODK.

• (Nothing yet)

[matthew-white]

@ktuite, you wrote at #1607 (comment):

Note for our future selves next release: we could start by adding a changelog to the docs at the start of the release. I didn't put things in the changelog when I filled out other parts of the API docs because it didn't exist yet and I didn't want to make a merge conflict. If the template existed already, I would have probably filled it in.

Do you still think we should add the changelog now? Would you be interested in doing so?