Backport: fix(mcp): deduplicate auth refresh on http transport

[github-actions]

This is an automated backport of #15518 to the release-v6.0 branch. FYI @aayush-kapoor
This backport has conflicts that need to be resolved manually.

git cherry-pick output

Auto-merging packages/mcp/src/tool/mcp-http-transport.test.ts
CONFLICT (content): Merge conflict in packages/mcp/src/tool/mcp-http-transport.test.ts
Auto-merging packages/mcp/src/tool/mcp-http-transport.ts
error: could not apply 6c17a9fe1... fix(mcp): deduplicate auth refresh on http transport (#15518)
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"

[github-actions]

🚀 Published in:

Package	Version
@ai-sdk/black-forest-labs	1.0.34 github npm
@ai-sdk/mcp	1.0.43 github npm