Use kernel-load in import-kernel-struct accessors (issues #16, #18)

import-kernel-struct generated accessors that expanded to direct
(load type ptr offset), which is only valid for verifier-trusted
pointers. Kernel pointers from get-current-task or probe-read-kernel
were silently rejected by the BPF verifier at load time.

Switch the generated accessors to use kernel-load, which emits
probe-read-kernel into a stack buffer. This makes imported kernel
struct accessors safe by default for kernel pointer traversal.

Closes #18
Closes #16

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>