fix(types): add [number, number] tuple support for line and scatter chart defaultDataPoint

[subodhbhyri]

Problem

When using an array of tuples ([number, number][]) as dataset data on a line
or scatter chart, TypeScript raises:

Type '[number, number]' is not assignable to type 'ScatterDataPoint | number | null'

This is despite tuples being a documented data structure
and already being supported for bar charts via [number, number] in its defaultDataPoint.

Fixes #12232

Changes

• Added [number, number] to defaultDataPoint for line and scatter in src/types/index.d.ts, matching the existing bar chart behavior
• Added type test cases in test/types/dataset_null_data.ts and test/types/data_types.ts to cover both ChartDataset and full new Chart(...) instantiation with tuple data

Scope

This PR fixes the TypeScript type error only. The runtime issue (line not
rendering when parsing: false is set with tuple data) is a separate problem
in the data parsing pipeline and is not addressed here.