feat: Improve cache size presentation and specification

feat: Improve cache size presentation and specification

Aligned how cache size is presented (in "ccache --show-stats", "ccache
--show-compression", "ccache --recompress", debug logs, etc.) and
specified (in configuration files, "ccache --max-size" and "ccache
--trim-max-size"). The size units are now formatted according to the
type of size unit prefix used for the max_size/CCACHE_MAXSIZE setting: a
decimal size unit prefix (k/M/G/T with or without B for bytes) in
max_size means using decimal size unit prefix for presented sizes, and
similar for binary size unit prefixes (Ki/Mi/Gi/Ti with or without B for
bytes). If no unit is specified, GiB is assumed, . For example, "ccache -M
10" means 10 GiB.

Also aligned how cache sizes are calculated. Now all sizes are computed
as "apparent size", i.e., rounded up to the disk block size. This means
that the cache size in "--show-stats" and the sizes presented in
"--show-compression" and "--recompress" now match.