Expose ada_get_version

[bbayles]

This PR adds ada_url.get_version, which currently returns '3.4.1'.

It also updates the license string, per this notice:

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            Please use a simple string containing a SPDX expression for `project.license`. You can also use `project.license-files`. (Both options available on setuptools>=77.0.0).

            By 2026-Feb-18, you need to update your project and remove deprecated calls
            or your builds will no longer be supported.

            See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
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