### What?
Upgrades sharp to the latest version and relies on more of its default
settings (if the default settings are unsuitable, we should consider
improving these for all users in sharp itself).
- The `sequentialRead` setting is now managed for you based on each
input image and the operations to be applied to it.
- The concurrency detection is more accurate than `os.cpus()` as it now
inspects things like CPU set/affinity as well as the memory allocator.
- The (mostly archaic) concept of chroma subsampling is not required for
AVIF output. Using full chroma should improve the quality of red/orange
edges, as well as slightly reducing file size as it allows greater use
of AV1 chroma-from-luma prediction.
In addition, this PR also enables the use of mozjpeg features such as
trellis quantisation to produce smaller file sizes. The use of `mozjpeg:
true` infers `progressive: true`. This aligns JPEG output behaviour with
the previously-used squoosh, which always used mozjpeg.
/cc @styfle
dd8ee527b8