chore: enable ruff's isort equivalent

[mistercrunch]

SUMMARY

Recently when I set up ruff (new linter/formatter that replaces black, isort, pyupgrade, ...) I didn't check that isort rules were enabled properly, this PR:

• enables the isort-like features
• configures them in ways that match the settings we had originally, minimize changes
• runs ruff check --fix with these new settings - everything here except a single change was auto-fixed in milliseconds

For the record, my configuration is based on the one suggested here -> astral-sh/ruff#4670 (comment)

For convenience, the list of all possible isort-related configs: https://docs.astral.sh/ruff/settings/#lint_isort_lines-after-imports.

Note that now that this is so fast and --fix works very well, it'd be easy to reconsider some configs if we wanted, for example setting lines-after-imports = 2 instead of -1 could be nice.