Claude review: gpu: nova-core: vbios: read BitToken using FromBytes

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

Patch Review

Good conversion. The manual byte-by-byte construction of `BitToken` is replaced with `FromBytes`, which is both safer and cleaner. Adding `#[repr(C)]` is required for `FromBytes` to have defined layout.

```rust
// SAFETY: all bit patterns are valid for `BitToken`.
unsafe impl FromBytes for BitToken {}
```

This safety comment is correct -- `BitToken` is `{u8, u8, u16, u16}`, all of which accept any bit pattern, and `#[repr(C)]` ensures the layout is predictable.

The checked arithmetic for `entry_offset` using `checked_mul`/`checked_add` is appropriate since both `token_size` and `token_entries` come from firmware.

**Minor note:** The original code checked `entry_offset + header.token_size > data.len()` but the new code uses `.get(entry_offset..).and_then(|data| data.get(..entry_size))` which achieves the same bounds check more idiomatically. However, if `entry_size < size_of::<BitToken>()`, `from_bytes_copy_prefix` will return `None` and the `.ok_or(EINVAL)?` catches it. This is correct.

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