Arcyd: limit landinglog to 1000 entries and rotate

To prevent unchecked growth of the landinglog, limit it to 1000 entries
and truncate the log if it grows larger than that, this should be
sufficient for a couple of months for a team that moves 100 reviews per
week.

Update write_log() to write lists of LogItem to simplify truncation.

Hide get_log_raw() to discourage breaking the abstraction.

Test Plan:
add exercise to breathing test (comment out due to long run time)
$ ./precommit.sh