feat(logs): Add better loading state for flex time strategy

[Zylphrex]

Previously, the flex time strategy could result in a really long loading state. This change shows a live progress with the bytes scanned in the loading state to indicate we're still working on it.

Closes LOGS-438

[linear]

LOGS-438 Show progress in incremental table scan

[sentry-io]

Bug: The useEffect accumulates bytesScanned multiple times for the same page due to lastPage reference changes on React Query state updates.
_{Severity: CRITICAL | Confidence: 1.00}

🔍 Detailed Analysis

The useEffect hook responsible for accumulating bytesScanned re-runs unnecessarily because its dependency, lastPage, receives a new object reference on every React Query state update, even if the underlying page data has not changed. This causes the bytesScanned value from the same page to be added multiple times to totalBytesScanned, leading to an inflated and incorrect total displayed to the user. This occurs whenever React Query updates its internal state, such as when isPending changes, triggering the effect with a new lastPage reference that points to the same data.

💡 Suggested Fix

Modify the useEffect to ensure bytesScanned is added only once per unique lastPage data object. This can be achieved by tracking a stable identifier from lastPage (e.g., lastPage.id or a unique hash of its content) and only performing the accumulation if this identifier has not been processed before.

🤖 Prompt for AI Agent

Fix this bug. In static/app/views/explore/logs/useLogsQuery.tsx at lines 587-606: The
`useEffect` hook responsible for accumulating `bytesScanned` re-runs unnecessarily
because its dependency, `lastPage`, receives a new object reference on every React Query
state update, even if the underlying page data has not changed. This causes the
`bytesScanned` value from the same page to be added multiple times to
`totalBytesScanned`, leading to an inflated and incorrect total displayed to the user.
This occurs whenever React Query updates its internal state, such as when `isPending`
changes, triggering the effect with a new `lastPage` reference that points to the same
data.

_{Did we get this right? 👍 / 👎 to inform future reviews.}