`RichString_appendnAscii()` avoids a `strlen(3)` call over
` RichString_appendAscii()`.
Use the former where the length is available from a previous checked
`snprintf(3)` call.
Keep `RichString_appendAscii()` when passing a string literal and
rely on compilers to optimize the `strlen(3)` call away.
`ZFS_RATIO` in `CRT.c` was unused, because I forgot
to colorize the ARC ratio in the Compressed ARC meter.
The intent was to improve readability of the meter by
highlighting the most relevant value, the ratio, in
a brighter color, for most themes. This change effects
that intent.
RichString_writeFrom takes a top spot during performance analysis due to the
calls to mbstowcs() and iswprint().
Most of the time we know in advance that we are only going to print regular
ASCII characters.
