slog-configurator v1.5.0 — Size and Len

logring.Handler.Size() reports the bytes the retained records occupy, and Len()
reports how many records that is. Stats already returned both alongside the drop
count; these are the single-value forms, so reading one number no longer means
destructuring a three-value return.

Size is the number the ring bounds itself by, so it is what to compare against
Options.MaxBytes and what decides when eviction starts. It counts the line, the
message and the attributes -- everything an entry retains.

A record refused for exceeding MaxRecordBytes is counted by neither.