Fix delayed swap info refresh on progress events

[lh-0610]

The swap info refresher wrapped a 3s debounce inside a 2s throttle. The throttle released a call every 2s and each release reset the debounce timer. Because 2s < 3s the timer never expired while progress events kept arriving, so the GUI stopped refreshing for as long as the swap kept making progress.

A single isolated event still waited 3s, and after the last event of a burst the refresh took up to 5s: up to 2s for the throttle trailing edge plus the 3s debounce window.

Drop the inner debounce and keep only the 2s throttle with its existing leading and trailing edges. The first event now refreshes immediately, rapid events coalesce, a continuous stream refreshes every 2s, and the final event is not lost. The throttle layer is unchanged, so no refresh can land later than it did before.

The throttle stays to rate limit the backend: each refresh issues both getSwapInfo and getSwapTimelock.

Extract the factory into swapInfoUpdater.ts. storeListener.ts pulls in the whole Tauri RPC and Redux graph, which cannot be imported into a unit test without heavy mocking.

Add three tests: the first event refreshes immediately, rapid events collapse into one leading plus one trailing refresh, and a continuous event stream keeps refreshing instead of stalling. The last one is the regression test for this bug.

AI usage disclosure
GPT-5.6-sol-high was used for code analysis, while Claude-opus-5 was used for code review and testing.

Closes #822

[binarybaron]

LGTM!

[lh-0610]

Thank you for reviewing and merging the PR!

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44cr7E1RS3YgyTXmmTPj2UPUdKvKZAvw5LoNeaDEQUDq893e6aLVtCUPv2XEWs9kKjd5E3N7sRtFuREpo5e3YNkzMAhiwVX