selftests/bpf: Add testcases for BPF_ADD and BPF_SUB

selftests/bpf: Add testcases for BPF_ADD and BPF_SUB

The previous commit improves the precision in scalar(32)_min_max_add,
and scalar(32)_min_max_sub. The improvement in precision occurs in cases
when all outcomes overflow or underflow, respectively.

This commit adds selftests that exercise those cases.

This commit also adds selftests for cases where the output register
state bounds for u(32)_min/u(32)_max are conservatively set to unbounded
(when there is partial overflow or underflow).

Signed-off-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Co-developed-by: Matan Shachnai <m.shachnai@rutgers.edu>
Signed-off-by: Matan Shachnai <m.shachnai@rutgers.edu>
Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250623040359.343235-3-harishankar.vishwanathan@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>