[Tracking Issue] Refactor `LowerSparseIter` pass

[yzh119]

Pitch

The current implementation of sparse iteration lowering, also known as the LowerSparseIter pass, was written in a single pass manner.

The IterTransformer mutator performs all the rewrites and it's error-prone and hard to maintain. We should refactor the pass to several smaller passes that perform a sub-step of the whole pass:

1. Auxiliary Buffer Materialization
2. Nested Loop Generation
3. Nested Block Generation
4. Read/Write region analysis
5. Binary Search Block generation
6. Guard generation