[refactor] provide numColumns from the DataProvider

[severo]

see #449

[Copilot]

Pull request overview

Refactors internal table state so numColumns is sourced from DataProvider via context (per #449), instead of being passed down as a prop, reducing prop threading and helping minimize re-renders.

Changes:

• Add NumColumnsContext / useNumColumns() to DataContext, and provide the initial column count from DataProvider.
• Update ColumnWidthsProvider to consume numColumns from context; update HighTable to stop passing numColumns.
• Update tests to validate numColumns provisioning and adapt ColumnHeader tests to the new context dependency.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/providers/DataProvider.test.tsx	Extends provider tests to assert numColumns behavior (including immutability expectation).
src/providers/DataProvider.tsx	Provides numColumns via a new context, keeping the initial value stable per data instance.
src/providers/ColumnWidthsProvider.tsx	Removes numColumns prop; reads numColumns from DataContext.
src/contexts/DataContext.ts	Introduces NumColumnsContext and useNumColumns().
src/components/HighTable/HighTable.tsx	Stops passing numColumns into ColumnWidthsProvider.
src/components/ColumnHeader/ColumnHeader.test.tsx	Wraps tests with NumColumnsContext.Provider to satisfy new dependency.

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