The data structure of the `bi2.bin` file in which the simulated memory
size is set:

> **13.2  Disk header Information**
>
> this is loaded to the Address in `0x800000f4` when a disc is initialized by the IPL
>
> |  offset  | end | size | Description           |
> | :------: | --- | :--: | --------------------- |
> | `0x0000` |     |   4  | Debug-monitor Size    |
> | `0x0004` |     |   4  | Simulated Memory Size |
> | `0x0008` |     |   4  | Argument offset       |
> | `0x000c` |     |   4  | Debug flag            |
> | `0x0010` |     |   4  | Track Location        |
> | `0x0014` |     |   4  | Track size            |
> | `0x0018` |     |   4  | Countrycode           |
> | `0x001c` |     |   4  | ?                     |

See https://hitmen.c02.at/files/yagcd/yagcd/chap13.html#sec13.2.

Most GameCube games set the value to `24 MiB`, which matches the
physical memory size. Most Wii games set the value to `0 MiB` (unset).
The debug build of _Mario Kart: Double Dash!!_ is one game that sets the
value to `48 MiB`.

We often use game IDs in paths, so we should try to make sure path
traversal is impossible in game IDs. Admittedly, doing any kind of real
attack using the six bytes available in game IDs is unrealistic, but no
game ID should contain non-alphanumeric or non-ASCII characters anyway.

Might also fix https://bugs.dolphin-emu.org/issues/13982 by skipping
converting between encodings for game IDs.

This had to be in the header back when it was templated, but 083faa8b
made it not templated.