memory usage
- Conditionally allocate prefix buffers in `LeafNode` and introduce `PrefixInternalNode` to reduce memory overhead when prefixes are disabled.
- Bypass prefix calculation and logic entirely when `UsesPrefixes` is false.
- Add a binary search fallback for key scanning.
- Implement a dedicated `int` scanning fast-path, removing SIMD prefix usage from `IntStrategy`.
- Reorganize key strategies into separate files.
- Add a new benchmark project specifically for string keys.
