User-visible improvements

• Adds support for lambda functions in Tasklets
• Adds NoHash class to disable hashing for some arguments. This is in jug.unsafe as it can be used to fool Jug, but it can be useful when there are nuisance arguments that are not relevant for the task (e.g., number of threads)
• jug.file_store: create files with better permissions

Internal improvements

• Convert to pyproject.toml for building

Bugfixes

• Better error detection for permission problems
• Bugfix when using local imports and jug pack

This release drops support for versions of Python older than 3.7. Technically, it should still work, but they are too old to test in Github CI, so we will not support them.