Claude review: rust: doctest: add LocalModule fallback for #[vtable] ThisModule

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

Adds a dummy `LocalModule` to the doctest harness in `scripts/rustdoc_test_gen.rs`:

```rust
struct LocalModule;

use kernel::{
    str::CStr,
    ModuleMetadata,
    ThisModule,
};
use core::ptr::null_mut;

impl ModuleMetadata for LocalModule {
    const NAME: &'static CStr = c"rust_doctests_kernel";
    const THIS_MODULE: ThisModule = unsafe { ThisModule::from_ptr(null_mut()) };
}
```

**Observations:**

1. The SAFETY comment is correct — `try_module_get`/`module_put` handle null module pointers gracefully (they short-circuit on NULL). This is the same pattern used for built-in modules (`#[cfg(not(MODULE))]` path).

2. This ensures doctests that exercise `#[vtable]`-annotated traits compile correctly without a real `module!` invocation.

**No issues found.**

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Generated by Claude Code Patch Reviewer