Our models should be robust enough to translate a calendar

[gregtatum]

The models tend to break down when presented with single numbers, or lists of numbers.

For example de-en translates

1
2
3
4
5
6
7
8
9

as

1
2
3
4
5 5
6 6
7
8
9 9

While en-ca (which did not use opus cleaner) succeeds.

Here is an example of what calendars look like when the model can't handle this.

![screenshot of a calendar widget with repeated numbers]https://github.com/mozilla/firefox-translations-training/assets/1588648/28d570fe-cc11-42f3-b7ed-d314575bc5d8)

This page is pretty useful as an in-browser test: https://www.timeanddate.com/calendar/

[gregtatum]

This could be helped by num_mismatch in OpusCleaner, and probably #215.

[marco-c]

Sometimes I wonder if it makes sense to implement some hardcoded rules.