Allow configuring hover/tooltip delay and search radius

[sanghoonio]

Summary

The hover tooltip behavior on EmbeddingViewMosaic is intermittent — sometimes hovering over points shows the highlight circle and tooltip, sometimes it doesn't. This is caused by hardcoded values in the tooltip throttle and hit detection that aren't exposed as configurable props.

Root Cause

Two hardcoded values in the library cause inconsistent hover detection:

1. throttleTooltip delay (packages/component/src/lib/utils.ts, line 42-43)

let delayMS = 300;
let recentThresholdMS = 300;

The first hover after a period of inactivity has a 300ms delay. During that delay, if the cursor moves, the pending query is replaced — so fast mouse movement means tooltips never appear. Once a tooltip has been shown recently (within 300ms), subsequent hovers are immediate, which is why hover works consistently after the first successful tooltip.

2. queryClosestPoint search radius (packages/component/src/lib/embedding_view/mosaic_client.ts, line 221)

let rMax = unitDistance * 12;

The hit detection searches within a 12-pixel radius in data coordinates. At certain zoom levels or point densities, the nearest point may fall outside this radius, returning null. The lastDistance cache starts at 0 (skipped), so the first query only uses the 12px fallback.

Requested Change

Expose these as configurable options, either through EmbeddingViewConfig or as separate props on EmbeddingViewMosaic / EmbeddingView:

• tooltipDelay — delay in ms before showing tooltip on hover (default: 300)
• tooltipRecentThreshold — threshold in ms for "recently visible" fast-path (default: 300)
• hoverRadius — search radius multiplier for hit detection (default: 12)

Alternatively, a simpler disableHoverTooltip boolean prop would also be useful for cases where consumers want to suppress hover tooltips entirely (e.g., showing tooltips only on click/selection).

Context

We're using EmbeddingViewMosaic with ~50k points. Users experience the hover as unreliable — sometimes the highlight circle appears on hover, sometimes it doesn't, with no apparent pattern. The inconsistency is confusing.

[sanghoonio]

Related to #174 — likely the same root cause. The throttleTooltip running flag can get stuck if the async DuckDB query hangs, which would explain both the intermittent behavior described here and the "stops responding after repeated hovers" in #174.

[donghaoren]

The hover behaves like a tooltip as in many system UIs --- if there is no existing tooltip, and the user keeps moving the mouse, it won't trigger the initial tooltip (the reason is to avoid distracting tooltips while the user is just moving the mouse across the view). The tooltip shows up when the user places the mouse on a point and keep it there for a certain amount of time. So, if the tooltip doesn't show up, just stop moving the mouse around and keep it on the point of interest.