Why do we need to bump the patch version?

The pip resolver will put 25.2.0 (from pypi) over 25.2.0.dev0 (from pypi.anaconda.org) as it merges both index and picks the latest. pip-compile will always end up with the stable release without the bump.

Do we actually need a version number based on the latest release (and can we) or can we just set it to 100.0.0.dev0?

If we use, e.g., 25.02.1.dev0, then when we release scipp, the nightly packages become, e.g., 25.03.1.dev0. But downstream, the dependencies where locked to 25.02.1.dev0 and so will continue to (try to) install the old wheel. So it seems to me that picking a fixed version number that can never appear naturally works better.

Do we actually need a version number based on the latest release (and can we) or can we just set it to 100.0.0.dev0?

100.0.0.dev0 should be fine too! I just wanted to make it look close to the last release.