fix(react): cancel session account initialization on unmount

[Jr-kenny]

Problem

useSessionAccount already passed a cancellation ref through its funding poll, but nothing set it when the hook unmounted. A screen could leave while initialization kept polling, and a later funding note could still trigger a consume transaction.

Fix

The hook now marks in-flight initialization as cancelled from an unmount-only effect. The cleanup is separate from session restoration so a changing storagePrefix during rerenders does not cancel a live initialization. The regression test holds syncState() open across unmount and checks that no note lookup or consume submission happens afterwards.

Closes #288

Testing

The full React SDK suite passes with 62 test files and 846 tests. I also ran the React typecheck, lint, and package build. Lint reports the repository existing unused-disable warnings, with no errors.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Recheck cancellation after the note lookup

When unmount occurs while waitAndConsume() is awaiting getConsumableNotes(), this cleanup sets the ref, but the helper does not read it again before constructing and submitting the consume transaction. A funding note returned after unmount therefore still triggers precisely the transaction this change is intended to prevent; check cancellation immediately after the note lookup and cover that pending phase in the lifecycle test.

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