Module crypto::buf

std/crypto's slice-to-reference helpers. Internal: included by std/crypto's headers (std-private; not API).

std/crypto's public functions take []const unsigned char / []unsigned char; these turn a slice back into the reference the (reference, length) cores work on, checking a fixed-size buffer (key, nonce, tag, digest) is long enough — a short one is a bug, so it panics instead of reading or writing past the end.