fix: return nearest element from binarySearchNearest instead of window edge

[NemeZZiZZ]

Problem

binarySearchNearest narrows the window to ≤ 2 (up to three candidates: left, left+1, right) and then returns left unconditionally — the window's left edge, not the nearest element:

if (mid <= 2) { break }
}
return left

Verified by execution: [10, 20, 30, 40, 50], target 39 → returns index 2 (value 30) instead of 3 (value 40); target 100 → index 3 instead of 4.

Consumers: Chart.scrollToTimestamp (Chart.ts:1172), Chart.zoomAtTimestamp (Chart.ts:1202), Store.timestampToDataIndex (Store.ts:1061) — all land 1–2 bars off the requested timestamp.

Fix

After the loop, compare the remaining candidates in [left, right] (at most three) and return the one with the smallest distance to the target. Ties resolve to the lower index.

Verification

Fuzz against brute-force nearest, 5000 random strictly-increasing arrays (lengths 1–300, targets in/around/beyond range): 5000/5000 match, ties to the lower index. The audit examples: 39 → 3, 100 → 4, 21 → 1, exact hit 30 → 2.

Note: on arrays with duplicate keys the result is still an index at the minimal distance, but among ties spanning more than the final window any tied index may be returned (pre-existing behavior; irrelevant for bar timestamps, which are unique).