[3.13] gh-142527: Docs: Clarify that random.seed() discards the sign of an integer input (GH-142483) (#142971)

gh-142527: Docs: Clarify that random.seed() discards the sign of an integer input (GH-142483)

If *a* is an integer, the sign of *a* is discarded in the C source code. Clarify this behavior to prevent foot guns, where a common use case might naively assume that flipping the sign will produce different sequences (e.g. for a train/test split of a synthetic data generator in machine learning).
(cherry picked from commit 610aabfef2f90dc1a274703779615aa5b7fbbb3a)

Co-authored-by: Andrej <andrej.karpathy@gmail.com>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>