`bf16` by default, even in Python 🐍

Previously, on modern CPUs the USearch index would default to f16 IEEE 16-bit floating point numbers, when used through high-level bindings, like Python. That format is more common in the Pythonic ecosystem, and it's supported by NumPy. Still, it's much less efficient and harder to convert to/from f32. The alternative is to use bf16, which is more hardware friendly, and upcast to f32, when we need to export the data back to Python. That's the new default behavior.

What's Changed

• Default to bf16 by @ashvardanian in #465

Full Changelog: v2.13.5...v2.14.0