Resolve numpy 2.2.0 issues and unpin

[davidorme]

The numpy 2.2.0 update brings in some typing changes in floating dtypes that mypy then flags as errors. There are a lot of these new errors (~100) and there's some discussion about whether this is acceptable and whether numpy or mypy or both are the bad guy here.

Either way, we've temporarily solved this by pinning numpy <2.2 (see #365) but we should keep an eye on this and unpin that once a solution has settled down.

numpy/numpy#27957