Fix arrays being expanded without reason

[flying-sheep]

Fixes #42

before this fix

• 👍 arrays that we don’t sort behave as expected (i.e. only get expanded when longer than column_width), but
• 👎 arrays that we do sort are always expanded into multiple lines
• 👍 arrays are never collapsed, which helps with VCS diffs

after this change

• 👍 single-line arrays are expanded when their lines are longer than column_width
• 👍 arrays are still never collapsed

Tip

One great thing about this change is that it doesn’t affect formatting at all for people who already use pyproject-fmt. It only affects people who newly adopt it or newly manually added/collapsed arrays

---

I also added pretty-assertions to the dev dependencies, because I think everyone agrees that trying to interpret

thread 'tests::test_column_width' panicked at rust/src/main.rs:335:9:
assertion `left == right` failed
  left: "[build-system]\nbuild-backend = \"backend\"\nrequires = [ \"c>=1.5\", \"d==2\" ]\n\n[project]\nname = \"beta\"\nclassifiers = [ \"Programming Language :: Python :: 3 :: Only\", \"Programming Language :: Python :: 3.12\" ]\ndependencies = [\n    \"e>=1.5\",\n]\n"
 right: "[build-system]\nbuild-backend = \"backend\"\nrequires = [ \"c>=1.5\", \"d==2\" ]\n\n[project]\nname = \"beta\"\nclassifiers = [\n    \"Programming Language :: Python :: 3 :: Only\",\n    \"Programming Language :: Python :: 3.12\",\n]\ndependencies = [\n    \"e>=1.5\",\n]\n"

is much worse than seeing