Claude review: rust: bitfield: Add KUNIT tests for bitfield

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

Patch Review

**Review: Good test coverage**

The tests are well-structured and cover the key functionality comprehensively.

**Coverage highlights:**
- Single-bit fields with boolean semantics (`test_single_bits`)
- Multi-bit range fields with `with_const_*` setters (`test_range_fields`)
- Builder pattern chaining (`test_builder_pattern`)
- Raw value round-trip (`test_raw_operations`)
- All three storage types: u8, u16, u64
- Infallible `=>` conversion with `Priority` enum
- Fallible `?=>` conversion with `MemoryType` enum, including invalid value testing
- Overlapping fields (`priority` at 5:4 and `priority_nibble` at 7:4)

**Intentional overlap testing (interesting design choice):** The `TestControlRegister` defines overlapping fields:
```rust
5:4       priority => Priority;
7:4       priority_nibble;
```
The test at line ~2146 verifies that setting `priority_nibble` to `0xF` causes `priority()` to return `Priority::Critical` (because bits 5:4 = 0x3). This is good coverage of the overlap behavior.

**MemoryType field width mismatch (by design):** `MemoryType` has 4 variants (0-3) but the `mem_type` field is 4 bits (15:12), allowing values 0-15. The `?=>` conversion correctly returns `Err` for values outside 0-3. The test validates this at line ~2068-2071:
```rust
let invalid_pte = TestPageTableEntry::from_raw(raw);
assert_eq!(invalid_pte.mem_type(), Err(0x7));
```

**Minor observation:** The `Priority::from(Bounded<u16, 2>)` implementation at line ~1961 uses `value & 0x3` which is a bitwise AND with an integer literal via `Deref`. This is slightly redundant since `Bounded<u16, 2>` is already guaranteed to be in range 0-3, but it's harmless and makes the intent explicit.

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Generated by Claude Code Patch Reviewer