Introduced `Iterator` structs in `UnsafeBitSet` and `SpanBitSet`
to enable efficient traversal of set bits. Added `GetIterator`
methods to both structs to return iterator instances. Implemented
`NextSetBit` in `SpanBitSet` to support iterator functionality.
Changed constants in `UnsafeBitSet` from `private` to `internal`
for broader assembly access. Removed redundant methods from
`SpanBitSet` to streamline the API in favor of iterator-based
operations.
Updated constructors in `UnsafeSlotMap` and `UnsafeSparseSet` to
conditionally clear arrays based on `AllocationOption.Clear`.
Incremented assembly version to 1.2.7 to reflect these updates.
Misaki
4dd5d6f1c6