Single-source the version from pyproject.toml

[garrison]

This PR was generated by Claude Opus 5 under my guidance.

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The version was declared twice — once in pyproject.toml and again as a literal __version__ in python/__init__.py. A release required editing both, and either edit alone would leave the two disagreeing with no error to signal it.

This reads the version from the installed distribution metadata instead, leaving the [project] table in pyproject.toml as the single declaration:

from importlib.metadata import version

__version__ = version("sbd-eigensolver")

Note the argument is the distribution name (sbd-eigensolver), not the import name (sbd).

Why this direction

The other way to de-duplicate is to have pyproject.toml declare dynamic = ["version"] and read attr = "sbd.__version__". That was not taken here. It depends on setuptools statically AST-parsing the assignment; if setuptools ever falls back to importing the package to resolve the attribute, it would import sbd before the extension modules are built, and this __init__ loads the _core_* backends at import time. Deriving the runtime attribute from the metadata avoids any build-time import of the package.

What this gives up

sbd.__version__ now requires the distribution metadata to be present. That holds for both pip install . and pip install -e .. It would break only for a source tree placed on sys.path without being installed — which is not a working configuration for this package regardless, since the compiled _core_* modules must be built into the package directory; importing in that state already fails with RuntimeError: No SBD backends available.

A try/except PackageNotFoundError fallback was deliberately omitted: it would convert a loud, accurate failure into a silently wrong version string for a case that cannot arise in a working install.

Verification

Checked in a throwaway virtualenv against a minimal package reproducing the same name mismatch and layout (packages = ["sbd"], package-dir = {sbd = "python"}):

• pip install . → sbd.__version__ == "1.6.1"
• pip install -e . → sbd.__version__ == "1.6.1"
• bumping only pyproject.toml to 9.9.9 and reinstalling → sbd.__version__ == "9.9.9", confirming the value tracks the single declaration with no second edit

test/conftest.py already reads sbd.__version__ to build the pytest header, so the existing suite exercises this path on every run.