Backport: [v6.0] fix(react): use the latest transport in useChat instead of a stale one

[github-actions]

This is an automated backport of #16806 to the release-v5.0 branch. FYI @gr2m
This backport has conflicts that need to be resolved manually.

git cherry-pick output

Auto-merging packages/react/src/use-chat.ts
CONFLICT (content): Merge conflict in packages/react/src/use-chat.ts
Auto-merging packages/react/src/use-chat.ui.test.tsx
CONFLICT (content): Merge conflict in packages/react/src/use-chat.ui.test.tsx
error: could not apply 1a0240bb8e... [v6.0] fix(react): use the latest transport in useChat instead of a stale one (#16806)
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config set advice.mergeConflict false"