Add `Uint128Heap`, `Uint64Heap` & `Uint32Heap`

Add Uint128Heap, Uint64Heap and Uint32Heap next to existing Uint256Heap to benefit from packing.

[...]
    struct Uint128Heap {
        uint128[] tree;
    }
[...]
    struct Uint64Heap {
        uint64[] tree;
    }
[...]
    struct Uint32Heap {
        uint32[] tree;
    }

Most of the logic for all variants can be shared into a Heap.sol.eta.

Numbers from Claude:

Warm (build+drain, one tx), total gas vs `Uint256Heap`: **128 −31%, 64 −51%, 32 −61%**.

Cold per-op (`vm.cool` before each), insert / pop:

| width | insert | pop |
|------:|-------:|----:|
| 256 | 43,604 | 35,940 |
| 128 | 22,003 | 32,366 |
| 64  | 19,714 | 27,246 |
| 32  | 16,969 | 22,666 |

Start by reading the existing Uint256Heap implementation and the proposed Heap.sol.eta abstraction. Add Uint128Heap, Uint64Heap, and Uint32Heap alongside it, sharing the common heap logic, then verify that each variant supports the same operations and delivers the intended packed-storage behavior.