Wide architecture: `nint`/`nuint` should become synonymous to `long`

Wide architecture set in Cesium supports same type sizes and layouts for any hardware platforms.

The only problem remaining is that it's not the same for `nint` / `nuint`: these types will currently compile to `IntPtr` and `UIntPtr`, platform-dependent.

We should improve the spec and make them synonymous to `long` and `ulong` on the **wide** architecture.

No files or tests are named. Start by locating the wide-architecture specification and the type-mapping entry point for nint and nuint, then compare their current IntPtr and UIntPtr handling with long and ulong. Done means the wide architecture consistently treats both types as their corresponding fixed-width aliases and the relevant compiler checks pass.

Written by the indexing model from the issue text.