gguf : reject tensor size that wraps after padding (#26979)

GGML_PAD(nbytes, alignment) wraps to 0 when nbytes is within
(alignment - 1) of SIZE_MAX, which silently bypassed the size
overflow guard in gguf_init_from_reader. Reject the tensor before
padding when nbytes + (alignment - 1) would overflow.

Adds a test-gguf handcrafted case (F32, ne = [4, 2^30-1, 2^30+1, 1])
whose ggml_nbytes = 2^64 - 16 lands in the wrap window. Fails on
master, passes with the guard.