feat: adaptive_compact_number displayer with range-aware precision

[paddymul]

Summary

Add an adaptive_compact_number displayer that automatically picks the right compact precision based on the column's value range, so that values close together (e.g. 5.68B vs 5.60B) remain distinguishable.

Problem

The compact_number displayer (#597/PR #601) uses a fixed maximumFractionDigits: 1, which works well when values span a wide range (2.3B vs 30B → 2.3B / 30B). But when all values in a column are clustered (e.g. 5,682,123,830 to 5,600,123,123), they'd all display as 5.7B — losing the meaningful differences.

Expected behavior

For the narrow-range example above: 5.68B / 5.60B — keep the compact suffix (B) but increase decimal places until values are distinguishable.

Design

New displayer type: adaptive_compact_number

export interface AdaptiveCompactNumberDisplayerA {
    displayer: "adaptive_compact_number";
    // Optional override — if omitted, Python auto-computes from column stats
    fraction_digits?: number;
}

Separate from compact_number so the simple fixed-precision version remains available.

Python-side range analysis

Compute the required precision in the Python styling pipeline using existing summary stats (min, max, range). Pass a fraction_digits hint in displayer_args to JS.

Algorithm sketch:

1. Determine the magnitude bucket (K/M/B/T) from the column max
2. Divide column range by the magnitude divisor (e.g. range / 1e9 for B)
3. Pick fraction_digits = minimum digits such that range_in_bucket * 10^digits >= 1 (i.e. at least 1 unit of difference in the last displayed digit)
4. Clamp to a reasonable max (e.g. 4)

Auto by default, overridable

• If fraction_digits is omitted, Python computes it from column stats
• User can explicitly set fraction_digits to override the auto behavior

Tooltip

Same as compact_number — full precision value shown on hover.

Files to modify

• buckaroo/dataflow/styling_core.py — new TypedDict + union member
• packages/buckaroo-js-core/src/components/DFViewerParts/DFWhole.ts — new interface + union
• packages/buckaroo-js-core/src/components/DFViewerParts/Displayer.ts — new formatter that reads fraction_digits
• packages/buckaroo-js-core/src/components/DFViewerParts/gridUtils.ts — tooltip wiring (same pattern as compact_number)
• Python analysis class to compute fraction_digits from summary stats
• Tests

Related

• Add opt-in compact numeric formatter (3M, 5.7B) with full-value tooltip #597 / PR feat: add opt-in compact_number displayer (#597) #601 — compact_number (fixed precision, merged)
• bad default styling #595 — bad default styling (compact abbreviations requested)
• Follow-up: column width contention policy and toggleable style presets #596 — width contention policy