[refactor] create Wrapper and TableCornerProvider to avoid rerenders

[severo]

see #449

Create a new Wrapper component for the outermost div element. Note that it provides the PortalContainerContext (a reference to it used for the portals).

Move the table corner (top left cell) size to a provider.

This avoids rerenders if that cell is resized, separates concerns, and removes the need to drill props.

[Copilot]

Pull request overview

This PR follows issue #449 by splitting table-corner sizing concerns into dedicated contexts/providers and introducing a Wrapper component to host the portal container context, with the goal of reducing unnecessary re-renders and prop drilling in HighTable.

Changes:

• Added TableCornerSizeProvider + TableCornerSizeContext to store and expose the top-left “table corner” cell width/height and its setter via context.
• Updated TableCorner, Slice, ColumnWidthsProvider, and ScrollProvider to consume table-corner size via context rather than props/state lifted into HighTable.
• Introduced components/HighTable/Wrapper to own the outer container element + PortalContainerContext provider.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/providers/ViewportSizeProvider.tsx	Adds clarifying comment about clientWidth/clientHeight usage.
src/providers/TableCornerSizeProvider.tsx	New provider that stores table-corner width/height and exposes a setter via contexts.
src/providers/ScrollProvider.tsx	Replaces headerHeight prop with useHeaderHeight() from the new context.
src/providers/ColumnWidthsProvider.tsx	Replaces tableCornerWidth prop with TableCornerWidthContext consumption.
src/contexts/TableCornerSizeContext.ts	New contexts + hooks for table-corner width/height and setter.
src/components/TableCorner/TableCorner.tsx	Switches to useSetTableCornerSize() and passes the element to the setter.
src/components/HighTable/Wrapper.tsx	New outer wrapper that sets CSS vars and provides PortalContainerContext.
src/components/HighTable/Slice.tsx	Removes setTableCornerSize prop drilling into TableCorner.
src/components/HighTable/HighTable.tsx	Wires in TableCornerSizeProvider + Wrapper and removes local corner-size state.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.