feat: Pretty materialization

[CasperTeirlinck]

We use the console and markdown materializers often to present metrics directly to users (users use the CLI to print the results, and we also post the markdown table on PR's). While it is an easy way to iterate on the metrics like that, the presentation of these materializations can be improved imo.

For example we use a lot of boolean metrics as so called "healthchecks", which now show as 0 / 1 | boolean to the user. I'd like to propose a "pretty" flag to these materializers so they print for presentation to the users instead of the raw metric fields in table format (which remain ideal for machines).

The unit of a metric is a free text field on purpose, but the idea is that some well-known units deserve a nice presentation. For example:

• "boolean": ✓/✗
• "percent": %
• more?

Summary

Changes to the ConsoleMaterializer and MarkdownMaterializer:

• Add a Unit StrEnum with some well-know units (bool and percent atm) that are free to use when defining (custom) metrics.
• Add a pretty flag to the 2 mentioned materializers that toggles special formatting depending on the unit.
• Allow to select a subset of columns to show.

Some related changes:

• Update the checkup.yaml a bit
• Flipped some existing boolean metrics to be consistent in "1 is good" and "0 is bad"
• Split up test files, it was 1 file of 1000 lines

Examples

You can put this in the checkup.yaml to set the default:

materializer:
  type: console
  pretty: true # <--

A basic checkup run in this repo now gives (see new defaults in the yaml:

or as before checkup run --materializer console:pretty=false:

But the effect gives better when you have healthcheck-type metrics that are all boolean:

versus without the pretty flag and column filter: