Bump dependencies, release version 0.3.0

[stephenfin]

Thanks for packaging this. I was attempting to use it with uv dependencies headers e.g.:

#!/usr/bin/env python3
# /// script
# requires-python = ">=3.10"
# dependencies = ["seahash"]
# ///

# ... rest of script ...

...and received the following error:

❯ uv run migrate.py --help
  × Failed to download and build `seahash==0.2.0`
  ├─▶ Failed to parse:
  │   `/home/stephenfin/.cache/uv/sdists-v9/pypi/seahash/0.2.0/zrefLOCpiDg9UaObCS4kl/src/pyproject.toml`
  ╰─▶ TOML parse error at line 5, column 1
        |
      5 | [project]
        | ^^^^^^^^^
      `pyproject.toml` is using the `[project]` table, but the required `project.version`
      field is neither set nor present in the `project.dynamic` list

I've added this missing field, bumping the version to 0.3.0 in the process. I've also taken the opportunity to update all dependencies - rust and python - across the project and add a tox.ini file. I've done this on a commit-by-commit basis so you can drop anything you don't want to do, but I hope this should be relatively uncontroversial.