fix(web): add Safari fallback for requestIdleCallback (#9137)

* fix(web): add Safari fallback for requestIdleCallback

* fix(web): use globalThis in idle-task fallbacks

Switch idle-task fallback paths from window.* to globalThis.* so the
fallback no longer crashes in environments where window is undefined.
Also thread IdleRequestOptions through requestIdleFallback so the
caller's timeout hint is honored when falling back.

Addresses CodeRabbit review feedback on #9137.

---------

Co-authored-by: sriram veeraghanta <veeraghanta.sriram@gmail.com>