Performance regression in L2 distance calculation for uint8

The linalg benchmark `L2(uint8, scalar)` degraded between eb1df70 and c4086ca and the most likely culprit seems to be https://github.com/lance-format/lance/commit/7bf7e97f65b06db16058953a71c920e2241ad7c3

This may have been intentional.  The PR did improve safety and overflow checking.  There does not appear to be any impact on non-scalar paths.