Source distribution issues

[znicholls]

• The source distribution is including everything rather than only including src and the LICENCE. This will require editing something in pyproject.toml to tell meson python what to include in the source distribution (starting docs: https://mesonbuild.com/meson-python/how-to-guides/sdist.html)
• The source distribution does not have the locked targets. To fix this, we should add the locked targets in before committing the bumped version then remove them all again before committing the next commit (i.e. the commit after the commit that gets the version tag)