Claude review: rust: sync: lock: Add Lock::get_mut_pinned()

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

Patch Review

**Correctness: Good.** The implementation is sound.

The method provides `Pin<&mut T>` from `Pin<&mut Lock<T, B>>` without acquiring the lock, which is safe because `&mut` guarantees exclusive access. This mirrors `std::sync::Mutex::get_mut()` from the Rust stdlib.

```rust
pub fn get_mut_pinned(self: Pin<&mut Self>) -> Pin<&mut T> {
    // SAFETY: We return a pinned T, ensuring we don't move T.
    unsafe { self.map_unchecked_mut(|data| data.data.get_mut()) }
}
```

The safety of `map_unchecked_mut` relies on the returned reference pointing to structurally pinned data. Since `data: UnsafeCell<T>` is `#[pin]` in the `Lock` struct definition (line 119 of `lock.rs`), this is correct.

**Minor issues:**

1. **Commit message says "These two functions"** but only one function (`get_mut_pinned`) is added. Likely a leftover from an earlier revision:

   > These two functions are inspired by the Rust stdlib equivalent

2. **`#[inline(always)]` is arguably too strong.** The method is trivial and the compiler will almost certainly inline it without the hint. `#[inline]` would suffice and avoids forcing inlining in debug builds. Very minor nit.

3. The method is placed in the `impl<T: ?Sized, B: Backend> Lock<T, B>` block, which is correct — it works for unsized types and any backend.

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