Use bpf_probe_read_*_str for all string buffer reads

[Copilot]

bpf_probe_read_kernel/user does not NUL-terminate when truncating, so buffers read into data.path, data.message, and data.command could contain garbage when printed as C strings in user space.

Changes

• chapter7/hello.bpf.c — replaced bpf_probe_read_kernel/user with bpf_probe_read_kernel_str / bpf_probe_read_user_str for all data.path reads (kprobe_sys_execve, kprobe_do_execve, fentry_execve, tp_sys_enter_execve)
• chapter6/hello-verifier.bpf.c — replaced bpf_probe_read_kernel with bpf_probe_read_kernel_str for data.message in both the p != 0 and fallback branches
• Multiple files — removed superfluous & when passing array fields to BPF helpers (arrays already decay to pointers)

// Before
bpf_probe_read_user(&data.path, sizeof(data.path), pathname);

// After
bpf_probe_read_user_str(data.path, sizeof(data.path), pathname);

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[lizrice]

@copilot I approved this, what happens next?

[Copilot]

@copilot I approved this, what happens next?

Since this is a stacked PR on top of the errata branch, the next step is to merge the errata base PR first. Once that's merged into main, this PR's base will update and it can then be merged as well. You can merge this PR directly into errata if you'd like to keep the changes together, or wait for errata to land first.