Functions to compute L1 distance

Manhattan distance sometimes useful

https://github.com/google-research/google-research/tree/master/scann/scann/distance_measures/one_to_one
https://github.com/ydb-platform/ydb/tree/main/library/cpp/l1_distance

Already done for bit (hamming)

Start by reviewing the existing bit (Hamming) distance implementation and the linked ScaNN and YDB L1-distance implementations. Determine the intended numeric types, APIs, and supported architectures before defining the scope. Done means the requested Manhattan-distance functions are implemented consistently with the project's existing distance functionality and covered by appropriate tests.

Written by the indexing model from the issue text.