ui/db-console: fix duplicate TS query requests on dashboard switch

[dhartunian]

Note(davidh): this investigation, conclusions, and fix was done by Claude. Keeping a detailed transcript here for posterity. I believe it's correct after reviewing.

When switching dashboards via the dropdown on the Metrics page, time series queries were dispatched multiple times with different time windows, resulting in duplicate HTTP requests to /ts/query. This doubled the load on the time series infrastructure.

The root cause was a chain of events triggered by the dashboard switch:

1. ErrorBoundary uses key={pathname}, so the entire subtree unmounts and remounts when the dashboard path changes.

2. setClusterPath called history.push(path) without preserving query params, so ?preset=past-hour was lost from the URL.

3. On remount, TimeScaleDropdownWithSearchParams's useEffect([]) fired. With no URL params, the else branch called onTimeScaleChange(props.currentScale), which dispatched SET_SCALE with the already-current scale.

4. The SET_SCALE reducer set shouldUpdateMetricsWindowFromScale = true even though the scale hadn't changed.

5. MetricsTimeManager (mounted above the ErrorBoundary, stays alive) saw the flag, called setWindow with a new "now" timestamp T2 (slightly different from the existing T1).

6. MetricsDataProviders that already dispatched requests with T1 in componentDidMount now saw changed timeInfo (T2) and dispatched a second round of requests in componentDidUpdate.

7. The saga's delay(0) batching window collected both T1 and T2 requests, grouped them into separate batches by timespan, and sent multiple HTTP requests.

Three changes fix this:

• Preserve query params in setClusterPath by passing { pathname, search } to history.push instead of just the path string. This keeps ?preset=past-hour in the URL across dashboard switches.

• Skip the SET_SCALE dispatch in TimeScaleDropdownWithSearchParams when the URL has ?preset=X and the redux store already has the matching preset with a moving window.

• In the else branch (no URL params), call updateUrlParams instead of onTimeScaleChange to sync the URL without dispatching SET_SCALE.

Also removes a dead requests = [] assignment that cleared a function parameter after it was already consumed.

Fixes: #158507

Release note: None

Epic: None

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