Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>

Change Update.update_wave() to return the wave bounds that encompass
Updog's seed value instead of just the lower bound. This makes the
actual update 'wave' relevant to a given Updog easier to conceptualise.
With follow-on changes to update_ready() and jitter() this fixes an
issue where if Updog was in the "0th" wave (ie. no lower bound) it would
incorrectly assume it had to wait for the upper bound time, when it is
actually free to update.

Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>

Add a new test to check handling of max_version, update to reflect the
changes to wave representation,  and make some minor updates to other
tests.

Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>

Add the Wave enum which defines the wave for a given Updog seed as
either the Initial wave, a General wave, or the Last wave. The
associated functions has_started() and has_passed() use these types to
simplify the logic in jitter() and update_ready().

Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>