fix: use installed package version for /version endpoint

[Functionhx]

Fixes #1341

The /version endpoint currently returns a hardcoded version string. This changes version to read from importlib.metadata.version('chromadb') so it reflects the actual installed package version. Falls back to '0.0.0' if the package is not installed.

[claude]

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[eeshsaxena]

This looks correct to me. I confirmed the distribution name in pyproject.toml is chromadb, so version("chromadb") resolves the installed package version, and __version__ is what the /version endpoint (segment.py) and the client User-Agent header (fastapi.py/async_fastapi.py) report - so this makes all of them track the real installed version instead of a hardcoded string that drifts. The PackageNotFoundError -> "0.0.0" guard is the right shape.

One thing worth being aware of: the fallback path is hit when the package has no installed metadata - i.e. running straight from a source checkout without an install. A normal pip install/pip install -e . both write metadata, so version("chromadb") works there; it's only a bare source run that would now report 0.0.0 (previously it showed the hardcoded string). That seems like an acceptable trade for not letting the hardcoded value go stale, but flagging it in case any dev workflow relies on __version__ being meaningful without an install.

Deferring to the maintainers.

[Functionhx]

Thanks! Yeah, 0.0.0 is intentional — better than silently reporting a stale version after an upgrade. The bare-source case is pretty rare in practice. Happy to tweak if maintainers prefer something else.