commitlog: Add explicit track var for "wasted space" to avoid double counting
commitlog: Add explicit track var for "wasted space" to avoid double counting

Refs #9331

In segment::close() we add space to managers "wasted" counter. In destructor,
if we can cleanly delete/recycle the file we remove it. However, if we never
went through close (shutdown - ok, exception in batch_cycle - not ok), we can
end up subtracting numbers that were never added in the first place.
Just keep track of the bytes added in a var.

Observed behaviour in above issue is timeouts in batch_cycle, where we
declare the segment closed early (because we cannot add anything more safely
- chunks could get partial/misplaced). Exception will propagate to caller(s),
but the segment will not go through actual close() call -> destructor should
not assume such.

Closes #9598

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla