Migrate packaging to pyproject.toml

[bertrmz]

Current Behavior

Project uses setup.py with setuptools for packaging and metadata.

Desired Behavior

Use pyproject.toml for packaging.

Benefits & Value

Aligns with current Python packaging standards and with 1Password's own Connect SDK.

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Reference: How to modernize a setup.py based project

Additional information

Platform-specific wheel builds for UniFFI native binaries and Python 3.9–3.13 support need to be preserved. See #113 for prior discussion.