[HW] Add HWConstProp pass for inter-module constant propagation

[prithayan]

This PR adds the HWConstProp pass that performs inter-module constant propagation across hardware module boundaries in the HW dialect.

The pass uses the Sparse Conditional Constant Propagation (SCCP) with lattice-based analysis
Key Steps:

1. Initialization
   • Mark public module inputs as overdefined (can't be constant)
   • Discover constants from hw.constant operations
   • Mark external/generated module outputs as overdefined
   • Enqueue operations for propagation
2. Propagation
   • Process operations from two queues (overdefined first, then constants)
   • Propagate constants through:
     • Module outputs → instance results
     • Instance inputs → module arguments
     • Combinational operations (fold when possible)
   • Use lattice meet: unknown ⊔ constant = constant, constant₁ ⊔ constant₂ = overdefined
3. Cycle Handling
   • Mark remaining unknown values as overdefined
   • Re-propagate to fold newly-resolved constants
4. Folding
   • Replace SSA values with discovered constants
   • Remove dead operations