[mathiasrw]

Closes #743

Stacked on #750. Merge that first.

Change

• Biome in place of Prettier for formatting. yarn format runs biome format --write, and yarn test-format runs biome format.
• biome.json is the config from argmate. The only change is that the built bin/ is left out, next to dist/, as RexReplace builds into bin/.
• .prettierrc and .prettierignore are removed, and // prettier-ignore is now // biome-ignore format.
• The code is formatted with Biome. This is only formatting: the main change is that an arrow function with one parameter has no parentheses around it, as in argmate.

Good to know

• Biome does not format Markdown. Prettier did not either here, as *.md was in .prettierignore.
• The linter in the config is not run by any script yet.

[mathiasrw]

Replaced by a new PR built on the current main. This one was on an old base and conflicted in 10 files.