comark/metrics/unit-mismatch · Write a ::stats row's before and after in one unit

A row's change compares its before and after as written, so both must be in the same unit. A row in MB before and kB after would show a change that isn't true, so it shows none.

Incorrect

::stats
| Metric | Before | After |
| --- | --- | --- |
| Pond photo | 1.2 MB | 800 kB |
::

lint-comark example.mdexample.md:1:1 comark/metrics/unit-mismatch::stats 1, row "Pond photo": before is in MB and after in kB.Write both in the same unit.✖ 1 problem

Correct

::stats
| Metric | Before | After |
| --- | --- | --- |
| Pond photo | 1200 kB | 800 kB |
::

lint-comark example.md✔ No problems