Add opt-in independentColumnResizing so a resize drag changes only the dragged column

[relznot]

Current behavior

Column resizing is zero-sum. In DataTableResizableHeaderHandle, a drag grows the dragged column by shrinking its immediate right-hand neighbor by the same amount (setMultipleColumnWidths writes both {accessor, width} entries, delta clamped by Math.max(-maxShrinkCurrent, Math.min(deltaX, maxShrinkNext))). Two consequences:

1. Widening a column crushes the neighbor, so laying out a wide table means fixing every column downstream of the one being adjusted — each fix steals from the next.
2. The last column can't be resized at all. Two independent gates enforce this: DataTableHeader strips the prop from the final leaf column (resizable={resizable && index < columns.length - 1}), and the handle's mousedown bails when there is no next resizable sibling to take width from.

Use case

Operators arranging a wide, horizontally-scrolling data table want to size one column without disturbing a layout they already set, and want to widen a column into the existing horizontal scroll rather than at a neighbor's expense. They also expect the rightmost column to be resizable like any other.

Proposed semantics — new opt-in DataTable prop independentColumnResizing?: boolean (default false, preserving today's behavior)

When enabled:

• A drag writes only the dragged column's width, clamped against its own min width with no upper bound.
• The table's total width (already the sum of pixel widths under the fixed-layout lock) grows or shrinks into horizontal overflow; neighbors are untouched.
• Both last-column gates are dropped, so the rightmost column is resizable.
• Release persists only the dragged column's width.
• Double-click-to-reset and reset-columns restore the fluid auto layout unchanged.

Accepted trade-off: shrinking columns can leave blank space to the right of the table when the total drops below the viewport width.

We currently ship exactly this as a patch-package patch against 9.4.0 (verified working, including persistence and reset) and would prefer to adopt it as a first-class prop. Happy to open a PR.