build: remove Polars dependency and relock (#15404)

Polars only ships cp310-abi3 wheels, which are not loadable under the
free-threaded CPython the repo targets (.python-version = 3.14t). uv
therefore builds the ~3 MB Rust sdist from source on every uv.lock
change, making CI builds very slow. Upstream (pola-rs/polars#27955)
is not yet ready to publish free-threaded wheels.

Remove polars from pyproject.toml and relock (uv sync --upgrade && uv lock).
No source files import polars, so nothing else changes.

Author: priya-sundaram-dev

pyproject.toml

@@ -22,7 +22,6 @@ dependencies = [
   "numpy>=2.1.3",
   "pandas>=2.3.3",
   "pillow>=11.3",
-  "polars>=1.44.2",
   "rich>=13.9.4",
   "scikit-learn>=1.9.1",
   "scipy>=1.18.1",