chore(v3): create ffi.py

Import close to 400 functions exposed by the Rust library into the
`ffi.py` file. All of them (save `version`) solely raise a
`NotImplementedError`. The documentation of the functions has been
automatically imported from the exposed docstring by the `pact.h`
header.

Some more minor changes includes:

- Adding the `py.typed` marker file (see [PEP
  561](https://peps.python.org/pep-0561/))
- Move all tests relating to `v3` into `tests/v3`
- Minor fixes toe the `ruff.toml` lint rules for tests
- Update type dependencies

Signed-off-by: JP-Ellis <josh@jpellis.me>