fix(python): validate BFloat16.from_bytes length

[ddupg]

Small fix for a missing return when BFloat16.from_bytes rejects non-2-byte input.

[claude]

Claude Code Review

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[yanghua]

If we can add some tests, e.g.

import pytest
from lance.arrow import BFloat16


def test_bf16_from_bytes_roundtrip():
    val = BFloat16(1.5)
    assert BFloat16.from_bytes(b"\xc0\x3f") == BFloat16(1.5)


@pytest.mark.parametrize("bad", [b"", b"\x00", b"\x00\x00\x00", b"\x00" * 4])
def test_bf16_from_bytes_invalid_length_raises(bad):
    with pytest.raises(ValueError, match="expected 2 bytes"):
        BFloat16.from_bytes(bad)

That would be better.

[ddupg]

If we can add some tests, e.g.

import pytest
from lance.arrow import BFloat16


def test_bf16_from_bytes_roundtrip():
    val = BFloat16(1.5)
    assert BFloat16.from_bytes(b"\xc0\x3f") == BFloat16(1.5)


@pytest.mark.parametrize("bad", [b"", b"\x00", b"\x00\x00\x00", b"\x00" * 4])
def test_bf16_from_bytes_invalid_length_raises(bad):
    with pytest.raises(ValueError, match="expected 2 bytes"):
        BFloat16.from_bytes(bad)

That would be better.

Thanks for reviewing, added tests.

[yanghua]

LGTM