bpf: signal error if old liveness is more conservative than new

bpf: signal error if old liveness is more conservative than new

Unlike the new algorithm, register chain based liveness tracking is
fully path sensitive, and thus should be strictly more accurate.
Validate the new algorithm by signaling an error whenever it considers
a stack slot dead while the old algorithm considers it alive.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250918-callchain-sensitive-liveness-v3-8-c3cd27bacc60@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>