We had some code in VolumeVerifier to catch the error message that
Redump.org used to show when trying to access the Wii datfile without
logging in. This restriction was removed from Redump.org around the
start of 2022, and the code has been unnecessary ever since.

sets defaults based on cpu support.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

This improves the speed of verifying Wii WIA/RVZ files.
For me, the verification speed for LZMA2-compressed files
has gone from 11-12 MiB/s to 13-14 MiB/s.

One thing VolumeVerifier does to achieve parallelism is to
compute hashes for one chunk of data while reading the next
chunk of data. In master, when reading data from a Wii
partition, each such chunk is 32 KiB. This is normally fine,
but with WIA and RVZ it leads to rather lopsided read times
(without the compute times being lopsided): The first 32 KiB
of each 2 MiB takes a long time to read, and the remaining
part of the 2 MiB can be read nearly instantly. (The WIA/RVZ
code has to read the entire 2 MiB in order to compute hashes
which appear at the beginning of the 2 MiB, and then caches
the result afterwards.) This leads to us at times not doing
much reading and at other times not doing much computation.
To improve this, this change makes us use 2 MiB chunks
instead of 32 KiB chunks when reading from Wii partitions.

(block = 32 KiB, group = 2 MiB)