In the last few PRs focused on improving dtypes there were a couple of comments that stud out as follow-ups:

1. Improve dtypes __repr__ (see test: Add serde tests for DTypes #3205 (comment))
2. Simplify __slots__ maintenance (see fix(expr-ir): Ensure only __slots__, and not __dict__ too #3201 and perf: Add __slots__ to all DTypes #3194 (comment))

Both these improvements can be achieved via a single metaclass.

I went ahead and started a branch (chore/dtype-meta) that mostly takes care of both, but it fails on typing (pyright is happy, mypy is not).

I will open a draft PR, but I am happy to keep this issue to discuss alternatives or reframe it if we need additional features