fix(series): non-finite values poison the axis domain and leak NaN into paths

[p32929]

Fixes #6.

The bug

Rendering two <Line> series where the second one has holes (the dataKey is missing on some
entries) produces NaN in the generated d attribute — and not only at the hole: every point on
that axis becomes NaN, so the whole chart disappears and the console fills with SVG errors.

Why

Two separate places let a non-finite value through.

1. lib/createSeries.ts — the axis domain is computed with Math.min/Math.max over the raw series.

const min = Math.min(...data, ...stackValues)
...
max = max ?? Math.max(...data)

accessData() returns undefined for an entry that does not have the key, and
Math.min(1, undefined) is NaN. So the axis registers {min: NaN, max: NaN}, scaleLinear
is built on a NaN domain in createPoints.ts, and every point it maps — including the
points of the other, complete series sharing that axis — comes back NaN. That is the part
that makes it look like the library cannot draw holes at all.

2. lib/utils.ts — pointDefined accepts NaN.

const pointDefined = (point: [number, number]) =>
  typeof point[0] === 'number' && typeof point[1] === 'number'

typeof NaN === 'number', so the gap-splitting logic in shapes/Curve.tsx — which is otherwise
completely correct and already supports connectNulls — never sees the hole, keeps the point in
the current segment, and hands NaN straight to d3's line().

The fix

• pointDefined checks Number.isFinite instead of typeof, so a missing point actually starts
  a new segment (or is dropped under connectNulls), which is what Curve.tsx already intends.
• createSeries filters non-finite values out of the values it feeds to Math.min/Math.max, and
  the stacked accumulator skips them too, so one series with holes can no longer poison the axis
  domain for every series on it.

No API change, no new option — connectNulls keeps its documented meaning and now actually works.

Reproducing

@stregouet's minimal repro is at https://github.com/stregouet/test-solidcharts — delete
data.value2 at one index and both lines vanish on main; with this patch the first line renders
normally and the second draws as two segments around the gap (or one continuous line with
connectNulls).