fix(price): stop order-status polling and setState after unmount (#2103)

* fix(price): stop order-status polling and setState after unmount

polling rescheduled timer.current inside the in-flight .then after the
cleanup already ran, leaking a 3s forever-poll and calling setState on
an unmounted component. Track a mounted ref and bail out of the .then
after unmount.

Fixes #2097

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: isolate payment polling generations

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Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: zgq <openai0229@gmail.com>