fix(vm_syscall): only extract input region for successful execs

[0xalpharush]

If a CPI call fails, Agave doesn't perform update_caller_account_region and the memory region may contain stale pointers. Given Agave doesn't read these in prod, it is fine. But the syscall harness is reading this intermediary state where there's a pending change (callee triggers realloc) that's never realized by the caller. One solution is to only call mem_region_to_input_data_region when the program returns StableResult::Ok.

Note, this will require updating test-vectors and FD's syscall harness.