Code coverage reports

[nonowazu]

Purpose
This adds code coverage reports

New Features
Code coverage, configured to maximum meanness - here's the output of the last result of coverage run -m unittest && coverage report:

Name                               Stmts   Miss Branch BrPart  Cover
--------------------------------------------------------------------
nari/__init__.py                       2      0      0      0   100%
nari/io/__init__.py                    0      0      0      0   100%
nari/io/reader/__init__.py            15      0      2      0   100%
nari/io/reader/pickle.py              14     14      0      0     0%
nari/io/writer/__init__.py            19     10      2      0    43%
nari/io/writer/pickle.py              12     12      0      0     0%
nari/types/__init__.py                 4      0      0      0   100%
nari/types/ability.py                  4      4      0      0     0%
nari/types/actioneffect.py            52     52      0      0     0%
nari/types/actor.py                   35     35      4      0     0%
nari/types/classjoblevel.py           33     33      0      0     0%
nari/types/director.py                68     68      4      0     0%
nari/types/event/__init__.py           6      0      0      0   100%
nari/types/event/ability.py           25     25      0      0     0%
nari/types/event/actorspawn.py         9      9      0      0     0%
nari/types/event/cast.py              29     29      0      0     0%
nari/types/event/config.py             8      8      0      0     0%
nari/types/event/death.py             10     10      0      0     0%
nari/types/event/effectresult.py      20     20      0      0     0%
nari/types/event/gauge.py             10     10      0      0     0%
nari/types/event/instance.py          41     41      0      0     0%
nari/types/event/limitbreak.py         9      9      0      0     0%
nari/types/event/markers.py           43     43      0      0     0%
nari/types/event/party.py              9      9      0      0     0%
nari/types/event/playerstats.py       25     25      0      0     0%
nari/types/event/status.py            24     24      0      0     0%
nari/types/event/statuslist.py        20     20      0      0     0%
nari/types/event/tether.py            11     11      0      0     0%
nari/types/event/ticks.py             19     19      0      0     0%
nari/types/event/updatehpmp.py        12     12      0      0     0%
nari/types/event/version.py           20     20      4      0     0%
nari/types/event/visibility.py        17     17      0      0     0%
nari/types/event/waymark.py           33     33      2      0     0%
nari/types/event/zone.py               8      8      0      0     0%
nari/types/job.py                     80     80      0      0     0%
nari/types/stats.py                   32     32      0      0     0%
nari/types/status.py                   9      9      0      0     0%
nari/util/__init__.py                  0      0      0      0   100%
nari/util/byte.py                     10     10      4      0     0%
nari/util/exceptions.py                5      5      0      0     0%
nari/util/pair.py                      9      9      2      0     0%
test/__init__.py                       0      0      0      0   100%
test/event/__init__.py                 7      0      0      0   100%
test/test_reader.py                   29      0      2      0   100%
--------------------------------------------------------------------
TOTAL                                847    775     26      0     9%

Bug Fixes
This is mentioned over in xivlogs/nari-act#3, but since that repo is undergoing some changes for rust, I thought I'd land it here first.

Before/After
Before:

hosakaii:nari king$ coverage
-bash: coverage command not found

After: see New Features, above

Additional Context
The word "empathy" did not enter the English language until 1908.

[ayyaruq]

It would be nice to see a future PR that gets this into PR comments so we can see changes nicely colourcoded.