Revert shuffle-based Vector.Reverse implementation

[Copilot]

This reverts c64060925b53a7ef24a796ed6e8c0e67ff95d49c, removing the shuffle-based Vector.Reverse<T> implementation introduced for the intrinsic vector types. The change restores the prior element-wise reversal behavior across the affected widths.

• Scope

  • Reverted the Reverse<T> changes in:
    • Vector64
    • Vector128
    • Vector256
    • Vector512

• Behavior

  • Restored the previous implementation strategy:
    • Vector64<T> uses the element-wise reverse loop
    • Wider vectors compose reversal from the next smaller vector width

• Result

  • Removes the recently introduced shuffle-based path without changing unrelated intrinsic APIs or helpers.